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.

Question: What is the third male reprodutive structure after the penis and testes? Answer: epididymis
Epididymis is the third male reprodutive structure after the penis and testes.

Question: How does the magnetic field produced by a current in a wire move? Answer: in concentric circles
The magnetic field produced by a  current in a wire moves in concentric circles.

Question: The mass of atoms is based on the number of protons and neutrons in what? Answer: nucleus

The mass of atoms is based on the number of protons and neutrons in nucleus.