**Core Concept**
Tuberculosis (TB) is a major public health concern, and understanding its transmission is crucial for prevention and control. The primary mode of TB transmission involves the inhalation of droplet nuclei containing Mycobacterium tuberculosis (M. tuberculosis) bacteria.

**Why the Correct Answer is Right**
The correct answer is that TB is primarily acquired through the respiratory route. When an individual with active pulmonary TB coughs, sneezes, or talks, they release droplets that contain M. tuberculosis bacteria. These droplets can remain suspended in the air for extended periods, allowing them to be inhaled by others. The bacteria then settle in the lungs, causing infection. The primary mechanism of TB transmission is through inhalation of these droplet nuclei, which can be as small as 1-5 micrometers in diameter.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because TB is not primarily spread through direct contact with an infected person. While direct contact can occur, the primary route of transmission is through the air.
**Option B:** This option is incorrect because TB is not primarily spread through contaminated food or water. While M. tuberculosis can be found in contaminated water, this is not the primary route of transmission.
**Option C:** This option is incorrect because TB is not primarily spread through vectors like mosquitoes or ticks. This mode of transmission is characteristic of other diseases, such as malaria or Lyme disease.

**Clinical Pearl / High-Yield Fact**
TB transmission can be prevented by using masks, improving ventilation, and treating individuals with active TB. The most effective way to prevent TB transmission is to treat individuals with active TB and to use effective infection control measures in healthcare settings.

**Correct Answer: D. Respiratory route.**