Given a scientific passage and an answer, generate a question for the given answer.
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Question: Passage: The last major ice age took place in the Pleistocene. This epoch lasted from 2 million to 14,000 years ago. Earth's temperature was only 5 C (9 F) cooler than it is today. But glaciers covered much of the Northern Hemisphere. In Figure below , you can see how far south they went. Clearly, a small change in temperature can have a big impact on the planet. Humans lived during this ice age. Answer: pleistocene

Answer: The last major ice age took place in which era?

Question: Passage: Destructive interference in waves occurs when two troughs overlap. Answer: two troughs

Answer: Destructive interference in waves occurs when what things overlap?

Question: Passage: Most natural gas comes from the wells that produce petroleum. An increasing amount comes from a new method. Hydraulic fracturing, called fracking , is very much in the news lately. Fracking makes it easier and quicker to get natural gas from the rock ( Figure below ). Answer: wells that produce petroleum

Answer:
Where does most natural gas come from?