Mirrors should be adjusted:

Before you start your trip.. Section 2.4: Adjust all mirrors before you start your trip.

Mirrors should be adjusted:

ANSWER BREAKDOWN
  • A. Incorrect. "While driving." is not correct. Adjust all mirrors before you start your trip.
  • B. Correct. Adjust all mirrors before you start your trip.
  • C. Incorrect. "Only if you can't see." is not correct. Adjust all mirrors before you start your trip.
  • D. Incorrect. "By your mechanic." is not correct. Adjust all mirrors before you start your trip.