The area of the lower limb that refers to the posterior side of the knee is the region.

popliteal

Explanation:

Popliteal refers to the hollow region of the lower limb present just behind the knee. In the popliteal region, the tendons of hamstrings are long and stringlike. The Popliteal region has a diamond-shaped space on the posterior side of the knee. This space is called the popliteal fossa. It is surrounded on the lateral side by the tendons of the biceps femoris muscle. In its medial position, the popliteal fossa is covered by the tendons of the semitendinosus and semimembranosus muscles.

i think that the best answer would be c.

tell me if im wrong : )