In what order will the cars pass through the junction if the police car (C) is driving with no beacons or siren on?

Explanation

With no special signals running, the police car (C) is just an ordinary road user. This is an unregulated junction of equal-priority roads, so the right-hand rule applies. The red car (A) goes first, as nothing is on its right. The blue car (B) follows, since its only obstacle on the right — red (A) — has already gone. The police car (C) waits for the blue car, which is on its right, so the police car (C) goes last.