To which skeletal system does the sternum belong?
a. spongy skeleton
b. compact skeleton
c. axial skeleton
d. appendicular skeleton

The correct answer is option D

The vertical, central axis of the human body is formed by the axial skeleton. It consists of 80 bones which include a skull, neck, chest, and back. It includes 22 bones of the skull, 6 bones of middle ears, 1 hyoid bone, 26 bones in the vertebral column, and 1 sternum, and 12 pairs or 24 ribs.  

Together with the appendicular skeleton (126 bones), it forms the complete skeleton.

gold i'm pretty sure i might be wrong