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

[EX Q]: Passage: Air movement takes place in the troposphere. This is the lowest layer of the atmosphere. Air moves because of differences in heating. These differences create convection currents and winds ( Figure below ). Answer: troposphere
[EX A]: What is the lowest layer of the atmosphere called?

[EX Q]: Passage: The way a mineral cleaves or fractures depends on the crystal structure of the mineral. Answer: the crystal structure
[EX A]: The way a mineral cleaves or fractures depends on what part of the mineral?

[EX Q]: Passage: Absorptive protists absorb food molecules across their cell membranes. This occurs by diffusion. These protists are important decomposers. Answer: diffusion
[EX A]:
Which process helps absorptive protists absorb food molecules across their cell membranes?