Question

what are the colors of the warning signs that indicate hazards ahead, such as curves in the road or narrow bridges? black letters or symbols on a white background. black letters or symbols on a yellow background. white letters or symbols on a blue background. white letters or symbols on a green background.

Explanation:

Warning signs for hazards like curves or narrow bridges (warning signs) typically use black symbols/letters on a yellow background. Regulatory signs use black on white, guide signs use white on green, and informational signs (like service) use white on blue. Hazard warning signs (like for curves) are yellow with black.

Answer:

Black letters or symbols on a yellow background.