I believe the correct answer is D.
"interaction between two different organisms living in close physical association, typically to the advantage of both"
.
so answer D matches the best.
The answer is synovial joints.
A synovial joint, also called diarthrosis, is present in the shoulders, hips, knees, elbows and wrist.
It has a fibrous joint capsule, a space between the bones that contains the synovial fluid and some of them can have additional structures.
There are six types of synovial joints and the shoulder or hip joints are called Ball and socket joints which allow all movements except gliding.
c would be your answer i just took the test
What 1 and 2 experiments?