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: Work is done only if a force is exerted in the direction of what? Answer: motion
[A]: Work is done only if a force is exerted in the direction of motion.


[Q]: Question: How many protons and electrons each do carbon atoms have? Answer: six
[A]: Carbon atoms have six protons and electrons each.


[Q]: Question: What do cells secrete that binds to receptors? Answer: factor
[A]:
Cells secrete factor that bind to receptors.