**Core Concept**
Sex determination in forensic anthropology is crucial for identifying human remains. The best bone specimen for sex determination is one that exhibits sexual dimorphism, which is the presence of distinct physical characteristics that differ between males and females. In the context of bone analysis, sexual dimorphism is often observed in the pelvis and femur.

**Why the Correct Answer is Right**
The correct answer is the pelvis. The pelvis is a key indicator of sex due to its larger size and wider subpubic angle in females. This is a result of the female pelvis being designed to accommodate childbirth. The female pelvis is also characterized by a wider pelvic outlet and a more pronounced sciatic notch, which is a groove for the sciatic nerve. These features are less pronounced in males, making the pelvis a reliable specimen for sex determination.

**Why Each Wrong Option is Incorrect**
**Option A:** The femur is a long bone that exhibits some degree of sexual dimorphism, but it is not as reliable as the pelvis for sex determination. Femoral length and diameter can be used to estimate sex, but these measurements can be influenced by age, ethnicity, and other factors.

**Option B:** The skull exhibits some sexual dimorphism, but it is not as reliable as the pelvis for sex determination. Skull features such as the mastoid process, nuchal crest, and orbital shape can be used to estimate sex, but these features are often subtle and can be influenced by various factors.

**Option C:** The humerus is a long bone that does not exhibit significant sexual dimorphism. While humeral length and diameter can be used to estimate sex, these measurements are not reliable and can be influenced by various factors.

**Clinical Pearl / High-Yield Fact**
When analyzing human remains for sex determination, it's essential to consider multiple specimens and use a combination of morphological and metric features to achieve accurate results.

**Correct Answer:** C.