When may you overtake another vehicle on the left?

Answer: C — if you are in a one way street, when the vehicle in front of you is signaling to the right, in slow moving traffic queues

Overtaking another vehicle on the left is generally not allowed unless it is a one-way street and the vehicle in front of you is signaling to turn right. This is because it is safer to pass vehicles on the right, and passing on the left can lead to accidents if the other driver is not expecting it. The other options are incorrect because A is too limited, B is incorrect as motorways usually have specific lanes for passing, and D is too extreme as there are certain situations where passing on the left is allowed.