**Core Concept**
Trichophyton species are a type of dermatophyte fungi that cause infections of the skin, hair, and nails. These fungi are keratinophilic, meaning they obtain their nutrients by breaking down keratin, a protein found in skin, hair, and nails.

**Why the Correct Answer is Right**
Trichophyton species infect the skin, hair, and nails by producing keratinases, enzymes that break down keratin into smaller peptides. This allows the fungi to obtain the necessary nutrients for growth and proliferation. The infection occurs when the fungi come into contact with the host's keratin-rich tissues, such as the skin, hair, or nails. The fungi then colonize the area, causing inflammation, itching, and other symptoms.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Trichophyton species are not known to infect internal organs, such as the lungs or liver.
**Option B:** This option is incorrect because while Trichophyton species can infect the skin, they are not typically associated with respiratory tract infections.
**Option C:** This option is incorrect because Trichophyton species are not known to cause infections in the gastrointestinal tract.

**Clinical Pearl / High-Yield Fact**
It's essential to note that Trichophyton infections, such as ringworm, can be transmitted through direct contact with an infected person or animal, as well as through contaminated objects or surfaces.

**Correct Answer:** C.