Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

[EX Q]: Oxygen gas is given off by plants.
[EX A]: Which gas is given off by plants?

[EX Q]: Sexual reproduction, in general, relies on sets of cells that are precursors for eggs and sperm.
[EX A]: What kind of reproduction, in general, relies on sets of cells that are precursors for eggs and sperm?

[EX Q]: Satellites are man-made devices in space that are used to observe the earth's surface.
[EX A]:
What man-made devices in space are used to observe the earth's surface?