Correct!

You're riding at night. You have your headlights on main beam. When should you dip your headlights if another vehicle overtakes you?

When the other vehicle signals to overtake
As soon as the other vehicle moves out to overtake
As soon as the other vehicle passes you
Correct answer
After the other vehicle pulls in front of you

DVSA theory test explanation

At night, you should dip your headlights to avoid dazzling oncoming drivers or those ahead of you. If you're being overtaken, dip your headlights as the other vehicle comes past. When you switch to dipped beam, your view of the road ahead will be reduced, so look ahead for hazards on your side of the road before you do so.