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

[EX Q]: Passage: tobacco smoke causes fatal lung disease in nonsmokers. Answer: tobacco smoke
[EX A]: What still causes fatal lung disease in nonsmokers?

[EX Q]: Passage: The cell membrane is made up of a phospholipid bilayer, two layers of phospholipid molecules. Notice the polar head group of the phospholipid is attached to the phosphate, and the tails are two fatty acid chains. The head group and tails are attached by a glycerol backbone. Answer: cell membrane
[EX A]: What basic cell structure is made up of a phospholipid bilayer and two layers of phospholipid molecules?

[EX Q]: Passage: Topographic maps have a horizontal scale to indicate horizontal distances. Answer: horizontal
[EX A]:
Topographic maps have a horizontal scale to indicate what distances?