Which of the following signals may be used to indicate a motorist’s intention to turn or change lanes?

Answer: C — Hand and arm signals

Hand and arm signals may be used to indicate a motorist's intention to turn or change lanes. This is because these signals can clearly and visibly communicate a driver's intentions to other motorists on the road. Option A, horn, may be used to warn others of danger, and option B, headlights, are used primarily for visibility purposes. While option D, brake light, does indicate that the vehicle is slowing down or stopping, it is not used specifically for signaling intent to turn or change lanes.