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

Q: Passage: and procaine. Not only do catalysts greatly increase the rates of reactions, but in some cases such as in petroleum refining, they also control which products are formed. The acceleration of a reaction by a catalyst is called catalysis. Answer: reactions

A: Catalysts can greatly increase the rates of chemical what?
****
Q: 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

A: What connects the fetus to the placenta?
****
Q: Passage: The process in which an atom becomes an ion is called ionization. It may occur when atoms are exposed to high levels of radiation or when atoms transfer electrons to or from other atoms. Answer: ionization

A:
What process can occur when atoms are exposed to high levels of radiation or when atoms transfer electrons to or from other atoms?
****