**Core Concept**
Trachoma is a chronic keratoconjunctivitis caused by the bacterium Chlamydia trachomatis, which is primarily transmitted through direct contact with an infected person's hands, clothing, or towels. The disease is a major cause of preventable blindness worldwide, particularly in areas with poor sanitation and limited access to healthcare.

**Why the Correct Answer is Right**
Trachoma is caused by serovars A, B, Ba, and C of Chlamydia trachomatis. These serovars are highly infectious and cause a prolonged asymptomatic carriage state, leading to repeated reinfection and transmission. The bacteria infect the conjunctival epithelium, leading to inflammation, scarring, and vision loss if left untreated. The serovars responsible for trachoma are distinct from those that cause genital Chlamydia infections (serovars D-K).

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because serovar D is associated with genital Chlamydia infections, not trachoma.
**Option B:** Incorrect because serovar L1a is a variant of serovar A, but the question asks for the primary serovar responsible for trachoma.
**Option C:** Incorrect because serovar L2b is associated with lymphogranuloma venereum (LGV), a different Chlamydia infection.

**Clinical Pearl / High-Yield Fact**
Remember that trachoma is a major public health problem in areas with poor sanitation and limited access to healthcare, and its prevention and treatment are key components of global blindness prevention efforts.

**Correct Answer:** C.