Let's go through the answer choices one by one:
A. False. The line segment contains more than just the endpoints
B. False. There are points in this description that extend beyond the endpoints. If this was a line instead of a segment, then choice B would be the answer
C. True. This is the answer. Though your teacher should have added "collinear" to the sentence to make it clear that the points are between M and N, and also collinear to M and N. All of these points form the line segment MN
D. False. That would be the perpendicular bisector of MN
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So once again, the final answer is choice C
