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: 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.

[EX Q]: Question: What do scientists think are the oldest eukaryotes? Answer: protists
[EX A]: Scientists think protists are the oldest eukaryotes.

[EX Q]: Question: Which acid releases nitrates into soil? Answer: uric
[EX A]:
Uric acid releases nitrates into soil.