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: Because trees add water vapor to air, cutting down forests leads to longer periods of what? Answer: drought
[EX A]: Because trees add water vapor to air, cutting down forests leads to longer periods of drought.

[EX Q]: Question: What do muscles need to contract? Answer: stimulus
[EX A]: Muscles need stimulus to contract.

[EX Q]: Question: When food enters the stomach after a period of fasting, a drop in what initiates the conversion of pepsinogen to pepsin? Answer: ph
[EX A]:
Ph food enters the stomach after a period of fasting, a drop in what initiates the conversion of pepsinogen to pepsin.