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

Input: Consider Input: The pressure of a sample of gas is measured with an open-end manometer.

Output: The pressure of a sample of gas is measured with an open-end what?

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: Planets are held by the force of gravity in elliptical orbits around sun.
Output: Planets are held by the force of gravity in elliptical orbits around what?