You want to turn left. When must you pay attention to the traffic following behind you?

You answered correctly. When turning left, you must always watch for traffic behind you both before moving into the left lane and just before making the actual turn. This ensures you do not endanger or hinder vehicles coming from behind, such as overtaking traffic or those that might not expect your maneuver. Checking after the turn is not necessary for this rule. Paying attention at both these points helps prevent accidents and keeps the turning process safe for everyone.