instruction:
Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
question:
Line graphs are especially useful for showing changes over time.
answer:
Line graphs are especially useful for showing changes over what?


question:
In the lungs, oxygen diffuses out of the alveoli and into capillaries.
answer:
In the lungs, oxygen diffuses out of the alveoli and into where?


question:
The term concentration describes the number of items in a given area or volume.
answer:

What term describes the number of items in a given area or volume?