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

Ex Input:
Passage: 41.4 Nitrogenous Wastes Ammonia is the waste produced by metabolism of nitrogen-containing compounds like proteins and nucleic acids. While aquatic animals can easily excrete ammonia into their watery surroundings, terrestrial animals have evolved special mechanisms to eliminate the toxic ammonia from their systems. Urea is the major byproduct of ammonia metabolism in vertebrate animals. Uric acid is the major byproduct of ammonia metabolism in birds, terrestrial arthropods, and reptiles. Answer: urea

Ex Output:
When vertebrate animals metabolize ammonia what is the primary byproduct that is produced?

Ex Input:
Passage: Alkenes are unsaturated hydrocarbons with at least one double bond between carbon atoms. Answer: alkenes

Ex Output:
What are unsaturated hydrocarbons with at least one double bond between carbon atoms called?

Ex Input:
Passage: Proteins are organic compounds made up of amino acids. Answer: amino acids

Ex Output:
What kinds of acids are proteins made out of?