**Core Concept**
Nasopharyngeal carcinoma is a rare type of cancer that originates in the nasopharynx, the upper part of the pharynx behind the nose. It is a unique entity with distinct epidemiological and demographic characteristics.

**Why the Correct Answer is Right**
Nasopharyngeal carcinoma predominantly affects the fifth decade of life, with a peak incidence in the 50-59 age group. This is attributed to the accumulation of genetic mutations and the prolonged exposure to environmental carcinogens, such as Epstein-Barr virus (EBV), which is a known risk factor for this malignancy. The EBV infection typically occurs in childhood, but the development of nasopharyngeal carcinoma requires a prolonged latent period, often spanning several decades.

**Why Each Wrong Option is Incorrect**
**Option A:** Children are not typically affected by nasopharyngeal carcinoma, as the disease has a long latency period and usually presents in adults.
**Option B:** Adolescents are also not commonly affected, as the peak incidence of nasopharyngeal carcinoma is in the fifth decade of life.
**Option C:** While nasopharyngeal carcinoma can present in the third decade, it is not the most common age group affected, as the peak incidence is in the 50-59 age group.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that nasopharyngeal carcinoma is strongly associated with Epstein-Barr virus (EBV) infection, particularly in endemic regions such as Southeast Asia and North Africa. The presence of EBV in tumor cells can be used as a diagnostic marker.

**✓ Correct Answer: D. 5th decade**