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

Ex Input:
Passage: Zinc reacting with hydrochloric acid produces bubbles of hydrogen gas. Answer: hydrogen

Ex Output:
Zinc reacting with hydrochloric acid produces bubbles of which gas?

Ex Input:
Passage: Producers are living things that use energy to make food. Producers make food for themselves and other living things. There are two types of producers:. Answer: producers

Ex Output:
Living things that use energy to make food, both for themselves and other living things, are what part of an ecosystem?

Ex Input:
Passage: Negative electrons are attracted to positive protons, and this electric force keeps electrons moving about the nucleus. The force of attraction between protons and neutrons, called the strong force, holds the nucleus together. Answer: positive protons

Ex Output:
What are negative electrons attracted to?