The height of the center of arm of a semaphore signal above the ground is A. 5.5 m B. 6.5 m C. 7.5 m D. 8.5 m

The correct answer is: C. 7.5 m

A semaphore signal is a type of railway signal that uses two arms to indicate the direction of travel. The arms are mounted on a post that is typically 7.5 m tall. The arms are painted red and white, and they can be moved up or down to indicate whether trains can proceed or must stop.

Option A is incorrect because the height of the center of arm of a semaphore signal above the ground is 7.5 m, not 5.5 m.

Option B is incorrect because the height of the center of arm of a semaphore signal above the ground is 7.5 m, not 6.5 m.

Option D is incorrect because the height of the center of arm of a semaphore signal above the ground is 7.5 m, not 8.5 m.