Final answer:
A person sits on the d) ischial tuberosity, which is the weight-bearing region of the pelvis when sitting and forms the posteroinferior part of the hip bone.
Step-by-step explanation:
A person sits on his or her ischial tuberosity. This large, roughened protuberance forms the posteroinferior portion of the hip bone and is the weight-bearing region of the pelvis when sitting. The hip bone consists of three main components: the ilium, pubis, and ischium, which converge to form the acetabulum, part of the hip joint.
The ilium forms the largest part of the hip bone and is firmly united to the sacrum at the sacroiliac joint. The ischium supports the body when sitting and features the ischial tuberosity and the ischial spine. Alternatively, the pubis makes up the anterior portion of the hip bone and joins the opposite pubis at the pubic symphysis.
The obturator foramen is a large opening between the ischium and the pubis, filled with connective tissue and used for muscle attachment. However, it is not the region that supports the body when sitting. Thus, the correct option in the final answer to the question "A person sits on his/her _____" is (d) ischial tuberosity.