In this task, you are given a question and an answer, you would be asked to create the sentence based on the Question-Answer provided. It should be contained within the Question-Answer provided.

[Q]: Question: The mass of atoms is based on the number of protons and neutrons in what? Answer: nucleus
[A]: The mass of atoms is based on the number of protons and neutrons in nucleus.

[Q]: Question: Which unit is used to express the amount of energy in food? Answer: Calorie
[A]: A calorie is used to express the amount of energy in food.

[Q]: Question: What man-made devices in space are used to observe the earth's surface? Answer: satellites
[A]:
Satellites are man-made devices in space that are used to observe the earth's surface.