**Core Concept**
The question is testing the knowledge of prophylactic measures against typhoid fever, specifically the use of antibiotics in asymptomatic carriers. The underlying principle is the prevention of typhoid transmission through the eradication of the carrier state.

**Why the Correct Answer is Right**
The drug of choice for carriers of typhoid is **Ciprofloxacin (C)**. This is because Ciprofloxacin is a fluoroquinolone antibiotic with broad-spectrum activity against gram-negative bacteria, including Salmonella Typhi. It is effective in eradicating the carrier state in asymptomatic individuals, thereby preventing the transmission of typhoid fever to others.

**Why Each Wrong Option is Incorrect**
* **Option A:** **Ceftriaxone (A)** is a cephalosporin antibiotic that is effective against a wide range of bacterial infections, but it is not the drug of choice for typhoid carriers. Ceftriaxone is typically used for the treatment of invasive salmonellosis or as an alternative in cases of fluoroquinolone resistance.
* **Option B:** **Amoxicillin (B)** is a penicillin antibiotic that has limited activity against gram-negative bacteria, including Salmonella Typhi. It is not effective in eradicating the carrier state and is therefore not the drug of choice for typhoid carriers.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the use of antibiotics in asymptomatic carriers of typhoid fever is a critical public health measure to prevent the transmission of the disease.

**Correct Answer:** C. Ciprofloxacin.