Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
--------
Question: You call a substance that is not an acid or a base neutral.

Answer: What do you call a substance that is not an acid or a base?

Question: Lipids are available to the body from three sources.

Answer: Lipids are available to the body from how many sources?

Question: Trees release oxygen gas as a byproduct of photosynthesis, thereby facilitating human respiration.

Answer:
Trees release what gas as a byproduct of photosynthesis, thereby facilitating human respiration?