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: When food enters the stomach after a period of fasting, a drop in what initiates the conversion of pepsinogen to pepsin? Answer: ph

SOLUTION: Ph food enters the stomach after a period of fasting, a drop in what initiates the conversion of pepsinogen to pepsin.

PROBLEM: Question: What do you call sound that has a wave frequency higher than the human ear can detect? Answer: ultrasound

SOLUTION: You call sound that has a wave frequency higher than the human ear can detect ultrasound.

PROBLEM: Question: What basic structure holds plants upright, bears leaves and other structures, and transports fluids between roots and leaves? Answer: stem

SOLUTION:
Stem basic structure holds plants upright, bears leaves and other structures, and transports fluids between roots and leaves.