What must you do when approaching a school bus with flashing red lights?

Answer: C — Stop, no matter what side of the road you are on

When approaching a school bus with flashing red lights, it is important to understand that the bus is either picking up or dropping off children and they may be crossing the road. Therefore, it is crucial to stop your vehicle to ensure the safety of these children. Option A and D are incorrect because increasing your speed or passing the school bus can be dangerous to the children and also illegal in many places. Passing the school bus on the left side, as mentioned in option B, is incorrect because the doors on the school bus open on the right side and children may be exiting or entering from that side. Hence, the only correct option is to stop, regardless of which side of the road you are on.