Final answer:
The best action when entering a curve with limited visibility of approaching traffic is to slow down and proceed with caution to ensure enough reaction time for any potential hazards.
Step-by-step explanation:
When entering a curve where it is difficult to see approaching traffic, the safest action to take is to slow down and proceed with caution. Increasing your speed can be dangerous as it reduces the time you have to react to unexpected hazards. Maintaining your speed might not be safe if your current speed does not allow for enough reaction time. Stopping and waiting for traffic to clear is not practical or safe in most driving situations, particularly when in an active lane where stopping could cause rear-end collisions. Therefore, the correct approach is to adjust your speed to ensure that you have ample time to react to any potential hazards that may arise as you navigate through the curve.