**Core Concept**
Human Immunodeficiency Virus (HIV) transmission occurs through various routes, including heterosexual contact. The virus primarily targets CD4+ T lymphocytes, compromising the immune system and leading to Acquired Immunodeficiency Syndrome (AIDS).

**Why the Correct Answer is Right**
During heterosexual transmission, the virus is primarily transmitted through vaginal or anal intercourse. The virus enters the body through mucosal surfaces, where it infects CD4+ T lymphocytes. The presence of HIV-1 antibodies in the blood and genital secretions indicates active infection. The risk of transmission is higher in individuals with higher viral loads, such as those with advanced HIV disease or those not on antiretroviral therapy (ART).

**Why Each Wrong Option is Incorrect**
* **Option A:** There is no evidence to suggest that HIV is transmitted through saliva or non-penetrative kissing.
* **Option B:** While HIV can be transmitted through breast milk, this is not the primary route of heterosexual transmission.
* **Option C:** HIV is not transmitted through casual contact, such as sharing utensils or swimming in a pool with someone infected with HIV.

**Clinical Pearl / High-Yield Fact**
The risk of HIV transmission can be significantly reduced through the use of antiretroviral therapy (ART), condoms, and pre-exposure prophylaxis (PrEP) in high-risk individuals.

**Correct Answer:** D.