The correct answer to this question is B, Yellow. The image shown is of a YIELD sign. The purpose of the sign is to alert the merging driver to stop to let another driver proceed. In other words, the yielding driver must do so to yield to the other vehicle, who has the right of way.
Yellow was the standard color for the Yield signs. It was this color for almost 20 years. Then, in 1971, the color of the sign changed to red. This is the color we still have today. The sign has a red background and has a white region at the center of the sign.