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

Ex Input:
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

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

Ex Input:
Passage: Improving crops by selecting for certain genetic traits. The desired traits promote productivity. Recently, genetically engineered crops have been introduced. Answer: promotes productivity

Ex Output:
What is the advantage of selecting for certain genetic traits for crops?

Ex Input:
Passage: Water is a common chemical substance on planet Earth. In fact, Earth is sometimes called the "water planet" because almost 75% of its surface is covered with water. If you look at Figure below , you will see where Earth's water is found. The term water generally refers to its liquid state, and water is a liquid over a wide range of temperatures on Earth. However, water also occurs on Earth as a solid (ice) and as a gas (water vapor). Answer: water

Ex Output:
What is a common chemical substance on planet earth?