Which of the following is a warning sign that may indicate a curve in the road?

The curve sign is specifically designed to alert drivers to an upcoming change in the road's direction, indicating that they should prepare for a curve ahead. This sign is typically shaped like a diamond and features a symbol or text that clearly states the nature of the curve, warning drivers to reduce speed and navigate the turn carefully to maintain safety.

In contrast, the straight road sign indicates a continuation of a straight path, which does not provide any information regarding changes in the road. The yield sign instructs drivers to give way to other road users but does not pertain to the road's curvature. The speed limit sign sets restrictions on how fast a vehicle can travel but does not indicate any upcoming road features like curves. Therefore, the curve sign is unmistakably the correct choice for indicating a road that will bend ahead.