Question

before changing lanes in traffic, you need to:
only check your rearview mirror
use arm signals
look over your shoulder to be sure the lane you want to use is clear
signal so that you have the right - of - way

Explanation:

• Checking only the rearview mirror is insufficient as it has blind spots.
• Arm signals are not typically used for lane - changing in modern traffic (except in specific situations like a broken turn signal, but it's not the main action).
• Signaling does not give the right - of - way; it just indicates intention.
• Looking over the shoulder (a visual check) helps to check the blind spot and ensure the lane is clear for a safe lane change.

Answer:

Look over your shoulder to be sure the lane you want to use is clear.