The bus driver brought the bus to a sudden stop.

a. active voice
b. passive voice

b. passive voice

I disagree.

It was not "The bus was brought to a stop by the driver".

You are correct, my apologies! The sentence is actually in the active voice, with the subject (the bus driver) performing the action (bringing the bus to a sudden stop).

The sentence "The bus driver brought the bus to a sudden stop" is in active voice.