Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

Q: For to synthesize glycogen purpose does liver use the excess carbohydrate.

A: For what purpose does liver use the excess carbohydrate?
****
Q: Natural resource type of resource is limited in supply and cannot be replaced except over millions of years.

A: What type of resource is limited in supply and cannot be replaced except over millions of years?
****
Q: When waves of two different frequencies interfere, beating occurs.

A:
When waves of two different frequencies interfere, what phenomenon occurs?
****