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

[EX Q]: Line graphs are especially useful for showing changes over time.
[EX A]: Line graphs are especially useful for showing changes over what?

[EX Q]: Through tubular ducts part do exocrine glands discharge their contents.
[EX A]: Through what part do exocrine glands discharge their contents?

[EX Q]: When light passes from one medium to another, it changes speed.
[EX A]:
When light passes from one medium to another, it changes what?