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

Example 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
Example Output: What connects the fetus to the placenta?

Example Input: Passage: When a fluorine atom gains an electron, it becomes a negative fluoride ion. Answer: fluoride ion
Example Output: When a fluorine atom gains an electron, it becomes a negative what?

Example Input: Passage: Heat waves have increased in frequency and duration in recent years. The summer 2011 North American heat wave brought record temperatures across the Midwestern and Eastern United States. Many states and localities broke records for temperature and for the most days above 100 o F. Answer: cell membrane
Example Output:
What are all cells surrounded by?