**Core Concept**
The hamstrings are a group of muscles in the posterior thigh that play a crucial role in knee flexion and hip extension. They are composed of three major muscles: the biceps femoris, semitendinosus, and semimembranosus.

**Why the Correct Answer is Right**
The biceps femoris is the most superficial muscle of the hamstrings and is responsible for knee flexion and hip extension. It is divided into two parts: the long head and the short head. The long head originates from the ischial tuberosity, while the short head originates from the linea aspera of the femur. The biceps femoris is innervated by the tibial nerve and is involved in various activities such as running, cycling, and jumping.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as the quadriceps are a group of muscles in the anterior thigh responsible for knee extension, not part of the hamstrings.
**Option B:** This option is incorrect as the adductor magnus is a muscle in the medial thigh responsible for hip adduction, not part of the hamstrings.
**Option C:** This option is incorrect as the gastrocnemius is a muscle in the posterior leg responsible for ankle flexion and plantarflexion, not part of the hamstrings.

**Clinical Pearl / High-Yield Fact**
The hamstrings are commonly injured in activities that involve sudden contractions, such as sprinting or jumping. The most common injury to the hamstrings is a strain, which can occur at the proximal, middle, or distal portions of the muscle.

**Correct Answer:** B.