**Core Concept**
Transvestism is a psychological phenomenon characterized by a recurring, intense urge to dress in clothing typically associated with the opposite sex. It is a form of cross-dressing and is often seen in individuals with gender dysphoria or other psychiatric conditions. The underlying concept being tested here is the classification and understanding of paraphilias.

**Why the Correct Answer is Right**
The correct answer, A. Wearing clothes of opposite sex, accurately describes transvestism. This behavior involves the voluntary assumption of the clothing, mannerisms, and other attributes typically associated with the opposite sex. Transvestism can be a coping mechanism for individuals dealing with gender dysphoria, anxiety, or other emotional issues. The behavior is often linked to the brain's reward system, releasing dopamine and providing temporary relief from stress or discomfort. In some cases, transvestism can be a symptom of an underlying psychiatric condition, such as schizophrenia or bipolar disorder.

**Why Each Wrong Option is Incorrect**
**Option B:** This option describes frotteurism, a paraphilia involving non-consensual touching or rubbing against others. It is not related to transvestism.

**Option C:** This option describes necrophilia, a paraphilia involving a desire for sexual intercourse with dead bodies. It is not related to transvestism.

**Option D:** This option describes voyeurism, a paraphilia involving the act of spying on others, often for sexual gratification. It is not related to transvestism.

**Clinical Pearl / High-Yield Fact**
Transvestism should be differentiated from transvestic fetishism, a condition where the act of cross-dressing is primarily for sexual gratification. In transvestism, the primary motivation is not necessarily sexual, but rather a desire to express oneself in a particular way.

**✓ Correct Answer: A. Wearing clothes of opposite sex**