On page 17, author Joey Bartolomeo writes “Caleb participated in the investigation by testifying about what happened during the health seminar at his school.” As it is used in that sentence, what does "testify" mean? *

C. to persuade someone to join a group
B. to disguise or hide from sight
A. to argue so as to make a person agree
D. to talk and answer questions about something after formally promising to tell the truth