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 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 signals the secretion of gastric acid? Answer: gastrin

SOLUTION: Gastrin signals the secretion of gastric acid.

PROBLEM: Question: When a fluorine atom gains an electron, it becomes a negative what? Answer: fluoride ion

SOLUTION:
When a fluorine atom gains an electron, it becomes a negative fluoride ion.