instruction:
Given a scientific passage and an answer, generate a question for the given answer.
question:
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
answer:
What term is defined as the ability to locate objects in the dark by bouncing sound waves off them.

question:
Passage: Momentum is a vector quantity that has the same direction as the velocity of the object. Answer: object ' s velocity
answer:
Momentum is a vector quantity that has the same direction as what?

question:
Passage: Polar climates are found near the North and South Poles. They also occur on high mountains at lower latitudes. The summers are very cool, and the winters are frigid. Precipitation is very low because it's so cold. The growing season is very short. Tundra prefers areas of permafrost. Permafrost is a lower layer of soil that is permanently frozen. Tundra also refers to a treeless plain with small plants. You can see examples of polar climates pictured below. Answer: permafrost
answer:
What do you call the lower layer of soil that is permanently frozen, and is a frequent feature of tundra?