Final answer:
The upper leg bone in the thigh is known as the femur, which is the longest bone in the human body and essential for supporting the body's weight.
Step-by-step explanation:
The name of the upper leg bone, in the thigh, is C) Femur. The femur is the single bone of the thigh and the longest bone in the human body. It is a critical component of the skeletal system, providing structural support and facilitating movement. Unlike the tibia and fibula, which are bones of the lower leg, the femur operates in conjunction with the hip joint and the knee joint, performing as the main support for the body's weight during locomotion.