What should a driver be cautious of when encountering a 'Merging traffic' sign?

Answer: C — Other vehicles entering the roadway from side streets

When encountering a 'Merging traffic' sign, it is important for a driver to be aware of other vehicles entering the roadway from side streets or merging from other lanes. This sign alerts drivers that the road ahead may become congested due to vehicles joining the traffic flow, which can happen when another road merges into the one you're traveling on. Being cautious in these situations involves being vigilant and ready to adjust your speed or position to allow merging vehicles to enter safely. Drivers merging onto a busy roadway may not have clear visibility or may misjudge the speed of oncoming traffic, so maintaining an awareness of their presence and being prepared to yield is crucial for preventing accidents. This context helps understand why it is essential to focus on merging traffic specifically, rather than being solely concerned with other potential hazards such as construction workers or other vehicles crossing the road.