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

Ex Input:
Natural resource type of resource is limited in supply and cannot be replaced except over millions of years.

Ex Output:
What type of resource is limited in supply and cannot be replaced except over millions of years?

Ex Input:
Clear mucus is secreted before ejaculation to neutralize acidic urine remaining in the urethra.

Ex Output:
What is secreted before ejaculation to neutralize acidic urine remaining in the urethra?

Ex Input:
Strong odor helps some animals defend themselves against predators.

Ex Output:
Which characteristic helps some animals defend themselves against predators?