**Core Concept**
The question is testing the ability to identify a specific opportunistic pathogen in HIV-infected individuals based on the presence of yeast-like morphology on Gram stain of lung aspirate. This requires knowledge of the common opportunistic pathogens associated with HIV/AIDS and their morphological characteristics.

**Why the Correct Answer is Right**
The presence of yeast-like morphology on Gram stain of lung aspirate in an HIV-infected individual is suggestive of Pneumocystis jirovecii pneumonia (PCP). P. jirovecii is an opportunistic pathogen that primarily affects individuals with compromised immune systems, such as those with HIV/AIDS. It is a unicellular fungus that can cause pneumonia, characterized by the presence of cysts and trophozoites in the lung aspirate. The yeast-like morphology is due to the trophozoite form of the organism, which is typically seen in the lung aspirate of patients with PCP.

**Why Each Wrong Option is Incorrect**
* **Option B:** Cryptococcus neoformans is a yeast-like fungus that can cause cryptococcal pneumonia in HIV-infected individuals. However, it typically presents with a different morphology on Gram stain, characterized by a large capsule and a narrow neck. Additionally, Cryptococcus neoformans is more commonly associated with meningitis and extrapulmonary infections in HIV-infected individuals.
* **Option C:** Histoplasma capsulatum is a dimorphic fungus that can cause histoplasmosis in HIV-infected individuals. However, it typically presents with a different morphology on Gram stain, characterized by small, intracellular yeast-like forms. Additionally, Histoplasma capsulatum is more commonly associated with pulmonary infections in immunocompetent individuals.
* **Option D:** This option is not provided.

**Clinical Pearl / High-Yield Fact**
In HIV-infected individuals, the presence of yeast-like morphology on Gram stain of lung aspirate should raise suspicion for Pneumocystis jirovecii pneumonia (PCP). PCP is a common opportunistic infection in HIV/AIDS, and prompt diagnosis and treatment are essential to prevent mortality.

**Correct Answer:** D