If the lower clamp screw is tightened and upper clamp screw is loosened, the theodolite may be rotated____________?

A. on its outer sdle with a relative motion between the vernier and graduated scale of lower plate
B. on its outer sdle without a relative motion between the vernier and gra-duated scale of lower plate
C. on its inner sdle with a relative motion between the vernier and the graduated scale of lower plate
D. on its inner sdle without a relative motion between the vernier and the graduated scale of lower plate