Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
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Question: When the smooth muscle relaxes, the arterioles dilate, allowing blood to enter the capillaries.

Answer: When the smooth muscle relaxes, the arterioles dilate, allowing blood to enter the what?


Question: Wave amplitude and wavelength are two important measures of wave size.

Answer: Wave amplitude and wavelength are two important measures of what?


Question: Star clusters are groups of stars called that are smaller than a galaxy.

Answer:
What are groups of stars called that are smaller than a galaxy?