What does a yellow traffic signal indicate to drivers?

Answer: A — Caution, the signal is about to turn red

A yellow traffic signal indicates that drivers should exercise caution because the signal is about to turn red. This means that drivers should slow down and prepare to stop if it is safe to do so. The purpose of the yellow light is to give drivers an opportunity to clear the intersection before the red light appears, ensuring that everyone on the road can navigate safely. The other choices do not accurately reflect the meaning of a yellow signal. Proceeding with full speed contradicts the intent of the cautionary signal, which is to prompt awareness and reduced speed. Preparing to turn left does not relate specifically to the meaning of the yellow light; it could apply in various situations but is not the primary purpose of the yellow light. Stopping immediately is not always advisable during a yellow light unless a driver is already too close to the intersection to safely do so. Therefore, caution is the best and most appropriate response when faced with a yellow traffic signal.