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.

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

[EX Q]: Question: When magma reaches the surface through cracks in the earth's crust, what occurs? Answer: volcanic eruption
[EX A]: When magma reaches the surface through cracks in the earth's crust, a volcanic eruption occurs.

[EX Q]: Question: Where does evidence that magnetic reversals occur come from? Answer: rocks on ocean floor
[EX A]:
Rocks on ocean floor is evidence that magnetic reversals occur.