When a school bus ahead of you has its red lights flashing, you should:

Answer: B — Immediately stop

When a school bus ahead of you has its red lights flashing, it is indicating that it is stopped and children are either getting on or off the bus. It is important to immediately stop and wait until the red lights have stopped flashing before proceeding. Option A, yielding to the bus, is not enough as you need to come to a complete stop. Option D, moving onto the shoulder, is also incorrect as this could be dangerous for both the children and other drivers. Similarly, option C is incorrect because you should not continue driving until the flashing lights have stopped and the bus has started moving again.