The correct answer is D. Femur.
The femur is the longest bone in the human body. It is also the strongest bone in the body. It is located in the upper leg and connects the hip to the knee. The femur is responsible for supporting the weight of the body and for allowing movement of the leg.
The tibia is the second longest bone in the body. It is located in the lower leg and connects the knee to the ankle. The tibia is responsible for supporting the weight of the body and for allowing movement of the leg.
The fibula is the third longest bone in the body. It is located in the lower leg and runs parallel to the tibia. The fibula is responsible for providing stability to the ankle joint.
The radius is the second longest bone in the forearm. It is located on the thumb side of the forearm. The radius is responsible for allowing movement of the wrist and hand.
The ulna is the third longest bone in the forearm. It is located on the little finger side of the forearm. The ulna is responsible for providing stability to the elbow joint.