Given a scientific passage and an answer, generate a question for the given answer.

[EX Q]: Passage: Relative dating determines which of two fossils is older or younger than the other but not their age in years. Relative dating is based on the positions of fossils in rock layers. Lower rock layers were laid down earlier, so they are assumed to contain older fossils. This is illustrated in Figure below . Answer: relative
[EX A]: What type of dating determines which of two fossils is older or younger than the other but not their age in years?

[EX Q]: Passage: Whales and bats have the trait of echolocation. This is the ability to locate objects in the dark by bouncing sound waves off them. The most recent common ancestor of whales and bats did not have this trait. Apply lesson concepts to explain how the trait evolved in whales and bats. Answer: echolocation
[EX A]: What term is defined as the ability to locate objects in the dark by bouncing sound waves off them.

[EX Q]: Passage: Most gemstones are not used exactly as they are found in nature. Usually, gems are cut and polished. Figure below shows an uncut piece of ruby and a ruby that has been cut and polished. The way a mineral splits along a surface allows it to be cut to produce smooth surfaces. Notice that the cut and polished ruby sparkles more. Gems sparkle because light bounces back when it hits them. These gems are cut so that the most amount of light possible bounces back. Other gemstones, such as turquoise, are opaque, which means light does not pass through them. These gems are not cut in the same way. Answer: opaque
[EX A]:
What are gemstones known as when light cannot pass through them?

