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

Ex Input:
Passage: The placenta allows nutrients and wastes to be exchanged between the mother and fetus. The fetus is connected to the placenta through the umbilical cord. Answer: umbilical cord

Ex Output:
What connects the fetus to the placenta?

Ex Input:
Passage: Solids have a fixed volume and a fixed shape. Liquids have a fixed volume but take the shape of their container. Gases take both the volume and the shape of their container. Answer: gases

Ex Output:
What takes both the shape and the volume of their container?

Ex Input:
Passage: Most hormones are controlled by negative feedback in which the hormone feeds back to decrease its own production. This type of feedback brings things back to normal whenever they start to become too extreme. Positive feedback is much less common because it causes conditions to become increasingly extreme. Answer: negative

Ex Output:
Most hormones are controlled by what type of feedback, which causes the hormone to decrease its own production?