Final answer:
The sacrum moves in the sagittal plane around an anterior-posterior axis, primarily performing flexion and extension movements.
Step-by-step explanation:
The sacrum moves in the sagittal plane, which divides the body into right and left sides. The type of movement it primarily performs is flexion and extension, which involve anterior (forward) and posterior (backward) movements. This motion occurs around an anterior-posterior axis. Therefore, the correct answer to the question 'In which plane and axis does the sacrum move?' would be A. Sagittal plane, anterior-posterior axis.