**Core Concept**
The question revolves around the modes of transmission of various diseases, with a focus on sexual transmission. **Sexually transmitted infections (STIs)** are a significant public health concern, and understanding their transmission dynamics is crucial for prevention and control.

**Why the Correct Answer is Right**
Since the correct answer is not provided, let's discuss a common disease not typically transmitted through the sexual route: **Hepatitis A**. This is primarily spread through the **fecal-oral route**, where the virus is ingested, often through contaminated food or water.

**Why Each Wrong Option is Incorrect**
**Option A:** Without the specific option, we can't directly address it, but diseases like **HIV** and **syphilis** are well-known to be transmitted sexually.
**Option B:** Similarly, **gonorrhea** and **chlamydia** are classic examples of STIs.
**Option C:** Diseases like **hepatitis B** can indeed be transmitted sexually.
**Option D:** Assuming this could be **hepatitis A**, it's the one that stands out as not primarily transmitted sexually.

**Clinical Pearl / High-Yield Fact**
Remember, while **hepatitis B** and **C** can be transmitted sexually, **hepatitis A** is more commonly associated with poor sanitation and hygiene, highlighting the importance of understanding the specific transmission routes of different diseases.

**Correct Answer:** D. Hepatitis A