**Core Concept**
Aspergillus is a type of fungus that can cause invasive aspergillosis, particularly in immunocompromised individuals. The pathogenesis of Aspergillus involves colonization of the lung, followed by invasion of the lung parenchyma. **The most probable portal of entry for Aspergillus is through the respiratory tract**, where the spores are inhaled.

**Why the Correct Answer is Right**
The correct answer is inhalation of Aspergillus spores. Aspergillus spores are ubiquitous in the environment and can be found in soil, decaying organic matter, and on plant material. When these spores are inhaled, they can colonize the lung, particularly in individuals with pre-existing lung disease or those who are immunocompromised. The spores can germinate and form a hyphal structure that invades the lung tissue, leading to invasive aspergillosis.

**Why Each Wrong Option is Incorrect**
* **Option A:** Ingestion of Aspergillus spores is not a common or significant route of entry for this pathogen.
* **Option B:** Skin inoculation with Aspergillus spores is not a typical route of entry, although it can occur in cases of trauma or skin breaks.
* **Option C:** The eyes are not a common portal of entry for Aspergillus, although ocular aspergillosis can occur in cases of trauma or immunocompromised states.

**Clinical Pearl / High-Yield Fact**
Aspergillus can cause a range of clinical conditions, from allergic bronchopulmonary aspergillosis (ABPA) to invasive aspergillosis, which can be fatal in immunocompromised individuals. **Early recognition and treatment of Aspergillus infections are critical to prevent morbidity and mortality**.

**Correct Answer: D. Inhalation of Aspergillus spores**