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

Q: The majority of human genes have two or more possible alleles.

A: How many possible alleles do the majority of human genes have?
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Q: Antibodies recognize and combine with harmful materials, including both toxic chemicals and invasive microorganisms.

A: Which proteins recognize and combine with harmful materials, including both toxic chemicals and invasive microorganisms?
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Q: Urea is made in the liver and excreted in urine.

A:
What is made in the liver and excreted in urine?
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