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

Ex Input:
Passage: An anticline is a fold that arches upward. The rocks dip away from the center of the fold ( Figure below ). The oldest rocks are found at the center of an anticline. The youngest rocks are draped over them at the top of the structure. When upward folding rocks form a circular structure, that structure is called a dome . If the top of the dome is eroded off, the oldest rocks are exposed at the center. Answer: anticline

Ex Output:
What is the term for a fold that arches upward?

Ex Input:
Passage: Mouth Brooding. Some species of fish carry their fertilized eggs in their mouth until they hatch. This is called mouth brooding. If you look closely, you can see the eggs inside the mouth of the cardinalfish pictured here. Answer: mouth brooding

Ex Output:
Some species of fish carry their fertilized eggs in their mouth until they hatch; this is called what?

Ex Input:
Passage: A caldera forms after a massive eruption. The top of the volcano collapses, forming a basin. Answer: after an eruption

Ex Output:
When does a caldera form?