A yellow triangle sign with a black border indicates:

Answer: B — railroad crossing

A yellow triangle sign with a black border typically indicates a railroad crossing ahead. The yellow color signifies caution, while the black border adds emphasis to the warning. This sign is often found on roads near or intersecting with train tracks. Option A, a no passing zone, is represented by a solid yellow line on a two-lane road. Option C, a sharp curve, is marked with a diamond-shaped yellow sign. Option D, an all-way stop, is marked with a red octagon sign. Therefore, it is important to pay attention to the specific shape and color of the sign in order to correctly identify its meaning.