**Core Concept**
Dermatophytes are a type of fungi that infect the skin, hair, and nails, causing conditions such as ringworm, athlete's foot, and onychomycosis. They obtain their nutrients by breaking down keratin, a protein found in the skin, hair, and nails.

**Why the Correct Answer is Right**
The correct answer is keratin, as dermatophytes secrete enzymes such as keratinases and proteases that break down keratin into smaller peptides and amino acids, allowing the fungi to obtain the necessary nutrients for growth and proliferation. This process is facilitated by the fungi's ability to invade and colonize the keratin-rich tissues of the skin, hair, and nails.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as dermatophytes do not primarily involve carbohydrates, which are the main energy source for many other types of fungi.
**Option B:** This option is incorrect as dermatophytes do not primarily involve lipids, which are an important component of the skin's barrier function but not the primary target of dermatophyte infection.
**Option C:** This option is incorrect as dermatophytes do not primarily involve nucleic acids, which are essential components of cellular DNA and RNA but not directly involved in the dermatophyte infection process.

**Clinical Pearl / High-Yield Fact**
It's essential to note that dermatophytes can be diagnosed through various methods, including microscopy, culture, and molecular testing, and treatment typically involves antifungal medications that target the fungal cell wall or inhibit the synthesis of ergosterol, an essential component of fungal cell membranes.

**Correct Answer:** C. Keratin.