TASK DEFINITION: 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.
PROBLEM: Question: What is at the top of the mesosphere? Answer: mesopause

SOLUTION: The mesopause is at the top of the mesosphere.

PROBLEM: Question: What is defined as the velocity of the object at a given moment? Answer: instantaneous velocity

SOLUTION: Instantaneous velocity is defined as the velocity of the object at a given moment.

PROBLEM: Question: What feature of the land do contour lines show? Answer: three-dimensional shape

SOLUTION:
Contour lines show the three-dimensional shape of land.