Given a fact, create a question that can be answered using the fact. Construct the question such that it is unambiguous, has a unique answer and the answer can be given using the fact.

Example Input: Fact: cycles of freezing and thawing water cause ice wedging
Example Output: Ice wedging is caused by cycles of freezing and thawing of what?

Example Input: Fact: lightning can cause a forest fire
Example Output: In a forest without anyone around, a fire may be started by?

Example Input: Fact: biofuel is used to produce electricity by burning
Example Output:
An example of biofuel could be?