Problem: Choose the next sentence
Seven years ago Sunday, American Bob Levinson disappeared after traveling to Iran. He's now one of the longest-held American citizens in history. Recently, the 65-year-old's family has said publicly that he worked for the CIA. Their decision to speak out came after news stories published in 2013 said Levinson worked for the spy agency. For years the family kept it quiet that Levinson was working for the CIA, because the United States government had warned them that revealing it would put Levinson in more jeopardy, they said. On Saturday, Levinson's son Dan Levinson talked in person with CNN in Abu Dhabi.

"We respectfully ask" the Iranian government to "work cooperatively with us" on the

Answer: Levinson investigation, Kerry said.


Problem: Choose the next sentence
ATHENS, Georgia (CNN) -- Over the railroad tracks, near Agriculture Drive on the University of Georgia campus, sits a unique machine that may hold one of the solutions to big environmental problems like energy, food production and even global climate change. Biochar's high carbon content and porous nature can help soil retain water, nutrients, protect soil microbes. "This machine right here is our baby," said UGA research engineer Brian Bibens, who is one of a handful of researchers around the world working on alternative ways to recycle carbon. Bibens' specialty is "biochar," a highly porous charcoal made from organic waste. The raw material can be any forest, agricultural or animal waste. Some examples are woodchips, corn husks, peanut shells, even chicken manure.

Biochar helps clean the air two ways: by preventing rotting biomass from releasing harmful CO2 into the atmosphere, and by allowing plants to safely store

Answer: CO2 they pull out of the air during photosynthesis.


Problem: Choose the next sentence
Stockholm, Sweden (CNN) -- A suspected serial shooter is keeping a city in southern Sweden on edge. Police say as many as 15 shootings in Malmo over the last year may be linked to a single perpetrator who is targeting immigrants living in the city. Investigators have no suspects. The shootings have all been well planned, under the protection of darkness and at places familiar to the shooter, according to CNN's Swedish affiliate TV4, citing police. Several of the shootings have occurred in recent weeks, police say. On Thursday evening, two immigrant women were wounded when shot through their apartment window.

The shootings also bring back memories of

Answer:
Sweden's "Laser-man," a shooter who was targeting immigrants in Stockholm in the 1990s with a laser-aimed rifle.