Given a context passage, generate a question from the passage such that its answer is shortest continous span from the passage.
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Question: A house of cards? Sounds unbelievable, doesn't it? Not if the architect is 31-year-old Bryan Berg. He's made a career out of building fantastic card houses, stadiums, capitols, castles -- and the world's tallest card tower. How does he do it? Bryan's structures are amazing because they are made entirely of perfectly balanced, freestanding playing cards. He never uses glue, tape, or anything else to hold the cards together. Nor does he fold the cards. He's discovered another way to make a strong house of cards, using a trick from nature. To make plants strong, nature builds them with cells that have tough walls. Rows and rows of these cells form a grid that helps leaves and stems keep their shape. Bees use the same kind of repeating pattern to create strong honeycombs, where they live and store honey. Bryan designs similar grids, using cards to create a repeating pattern of cells. He begins with a single cell made by balancing four cards against one another to form a box. Then he repeats the cell over and over, expanding outward to form the grid, which makes a good foundation for a strong card structure. The larger the grid, the more weight it can carry. Sometimes Bryan uses several cards, instead of just one, to construct the cell walls, making the grid even stronger. The trick, he tells kids when he speaks in classrooms, is to place your cards as tightly together as possible when laying out your grid, making sure the cards are not leaning at all. After building this solid base, Bryan lays cards across the top to make the floor for the next "story" of the building. He may add towers, columns, steeples, or domes. Using the principle of repeating cells, Bryan builds structures of amazing strength. In the Cards Not surprisingly, Bryan has always been interested in building things. Growing up on a "big, old farm" in rural Iowa, he had plenty of room to play. "We were in the middle of nowhere," Bryan remembers, "with lots of space to do whatever we wanted. I was always making something, using things like sticks or bales of hay." Bryan's grandfather taught him how to stack cards. Bryan's two interests -- building and card stacking -- soon combined. But stacking in his family's farmhouse was challenging. "Our old house had wood floors that weren't all level," he reports. "And they weren't very firm. When people walked around, it was like 'earthquake action.' It was a challenge to build something that wouldn't fall down immediately." Bryan constructed tower after tower; he went through a lot of trial and error before he built anything taller than himself. When he placed a few decks of cards on top of his grid, he discovered how strong it was. Bryan's towers began to grow taller. How Tall Is Too Tall? Bryan's first Guinness World Record for the world's tallest card tower came in the spring of 1992, when he was in high school. Learning that the world record was 12 feet 10 inches, Bryan built a slim tower that topped out at 14 feet 6 inches. Done as a project for his geometry class, it took him 40 hours and 208 decks of cards. Since then he's gone on to win world records for even taller buildings. His latest winner measured 25 feet 3.5 inches and used about 2,400 decks of cards. _ Why don't these towers fall down? The key is in a good solid base, a repeating pattern of stories, and a tapering top. Bryan likes to point out how card buildings resemble real ones. They are built cell by cell, story by story. The separate parts make one strong whole. The heavier the building, the stronger and more stable it is. But the weight can't all be at the top. After spending so much time building something so cool, Bryan admits it's sometimes painful to see his structures destroyed. But he compares his work to the building of a sandcastle or an ice sculpture.

Answer: What was Bryan's first world record?


Question: You're in your office when you learn there's someone with a gun wandering outside. You can hear gunshots and screams. What do you do? That's the challenge for users of a new virtual reality program called SurviVR, designed to train employees how to deal with an active shooter situation in the workplace. The program works with HTC Vive, the virtual reality headset released earlier this year. An active shooter situation is when an armed person or people actively shoot in a small, populated area with the intention to kill. There were 20 such situations in the United States last year and 20 the year before, according to FBI statistics, resulting in a total of 231 deaths. This year saw the deadliest active shooter situation in US history , with 49 people killed in a nightclub in Orlando. In the training situation, users have four choices. They can lock themselves in the office. They can hide, perhaps in the office closet. They can run for an exit. Or they can use something in the office--a computer or a cup a pair of scissors-as a weapon to fight the shooter. This is an improvement on standard active shooter training. Gallo says, which typically teachers people to lock themselves in place and hide. The "lock down" method is often ineffective, he says, and has resulted in many deaths in recent years. In the training's basic level, no one gets killed. But as the trainings become more advanced, players who make a wrong choice be shot. There's no blood; the screen simply turns black slowly. If this sounds terrifying, that's the point, says Gallo. There are plenty of training programs to teach employees how to deal with workplace violence, sometimes involving role play with toy guns. But these trainings are basically games. Gallo says, with employees relaxed and even enjoying themselves. To teach people what they really need to know for an active shooter situation, they need to be scared. "SurviVR will take the fear and turn it into confidence." Gallo says.

Answer: What does Gallo think of the training programs involving role play with toy guns?


Question: Human population growth over the past 10,000 years has been tremendous (Figure 1.1). The entire human popula- tion was estimated to be 5 million in 8000 B.C. 300 million in A.D. 1 1 billion in 1802 3 billion in 1961 7 billion in 2011 As the human population continues to grow, different factors limit population in different parts of the world. What might be a limiting factor for human population in a particular location? Space, clean air, clean water, and food to feed everyone are limiting in some locations. Not only has the population increased, but the rate of population growth has increased (Figure 1.2). The population was estimated to reach 7 billion in 2012, but it did so in 2011, just 12 years after reaching 6 billion. Human population from 10,000 BC through 2000 AD, showing the exponential increase in human population that has occurred in the last few centuries. The amount of time between the addition of each one billion people to the planets population, including speculation about the future. Although population continues to grow rapidly, the rate that the growth rate is increasing has declined. Still, a recent estimate by the United Nations estimates that 10.1 billion people will be sharing this planet by the end of the century. The total added will be about 3 billion people, which is more than were even in existence as recently as 1960.

Answer:
human population reached its first billion in which year?


