Answer:
B He was afraid and didn’t understand the reason he had to go.
Step-by-step explanation:
According to the text, Fred "couldn’t understand why his mom was insisting on taking him to the dentist." The reason is that his teeth did not hurt and he always took good care of them. However, after the initial terror, he was relieved because the dentist did not torture him and showed him how the correct way to brush and floss his teeth.