**Core Concept:** An X-linked dominant trait is a genetic disorder that affects individuals who inherit one abnormal gene from their affected parent and a normal copy of the gene from their non-affected parent. This type of inheritance follows the Mendelian ratio of 1:1 in offspring.

**Why the Correct Answer is Right:** Option D, **Xeroderma Pigmentosum Group C (XPC)**, is a correct answer because it is an X-linked dominant disorder. Individuals with XPC inherit one abnormal XPC gene from an affected parent and one normal XPC gene from a non-affected parent, leading to an 1:1 ratio in offspring.

**Why Each Wrong Option is Incorrect:**

A. **Familial Mediterranean Fever (FMF)** is an autosomal recessive disorder, meaning both parents must carry the abnormal gene for their child to inherit the disorder. In this case, the ratio would be 2:2, 1:1, or 2:1 depending on the parents' genotypes.

B. **Hemophilia A** is also an X-linked recessive disorder, which means that both parents must carry the abnormal gene for their child to be affected. The ratio would be 4:1 (2:1) for affected:unaffected sons and daughters.

C. **Marfan's Syndrome** is an autosomal dominant disorder, meaning that an affected parent can pass the disorder to one-half of their offspring (1:1 ratio). However, this option is incorrect as Marfan's Syndrome is not an X-linked disorder.

**Clinical Pearl:** It is essential for medical professionals to understand the inheritance patterns of different genetic disorders, as this knowledge impacts diagnosis, counseling, and management strategies for patients and their families. Familiarizing oneself with the Mendelian ratios for autosomal dominant, autosomal recessive, and X-linked dominant disorders will aid in the accurate interpretation of familial relationships and genetic testing results.