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

Input: Consider Input: When the smooth muscle relaxes, the arterioles dilate, allowing blood to enter the capillaries.

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


Input: Consider Input: A diet rich in calcium and vitamin d may reduce the risk of osteoporosis and related bone fractures.

Output: A diet rich in calcium and what vitamin may reduce the risk of osteoporosis and related bone fractures?


Input: Consider Input: Leaves changing color on trees of these is the best sign that the fall season has begun.


Output: Which of these is the BEST sign that the fall season has begun?