10. If you move at a very high speed towards a yellow traffic light you may see it as a

b. green traffic light

This is due to the Doppler effect: As you move towards the source of a wave (or if it moves towards you) the frequency of the wave that you detect (here with your eyes) is increased.

This is by far the hardest question in the quiz!

That's because in order to really see a yellow light appear green you need to move towards the light at 50,000 km/sec! That's somewhat over the speed limit...