D. to talk and answer questions about something after formally promising to tell the truth
Explanation:
The verb <em>testify </em>means to provide evidence and testimony as a witness in a court of law. In the passage, the author Joey Bartolomeo explains that Caleb takes part in the investigation about the health seminar. Thus, Caleb makes a formal deposition, which will be used to examine the facts and establish the truth.
“When they heard Box 342 rung, however, they assumed the fire was out of their territory and unhitched the horses. Only two fire companies were not fooled by the misleading alarm.”
