**Core Concept**
The question is testing the knowledge of the appropriate antibiotic treatment for primary syphilis, a bacterial infection caused by *Treponema pallidum*. The correct answer is based on the antimicrobial properties of the drug and its efficacy against this specific pathogen.

**Why the Correct Answer is Right**
The drug of choice for primary syphilis is benzathine penicillin G (BPG) due to its high efficacy and ability to penetrate the cerebrospinal fluid (CSF), which is essential for treating neurosyphilis, a potential complication of untreated syphilis. BPG is administered intramuscularly, providing a sustained release of penicillin over several days, which is crucial for eradicating the infection. The recommended dose is 2.4 million units administered as a single intramuscular injection.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as it does not specify the correct drug or dosage for primary syphilis treatment.
* **Option B:** This option is incorrect as it is not a first-line treatment for syphilis, although it may be used in some cases of penicillin allergy.
* **Option C:** This option is incorrect as it is not a standard treatment for primary syphilis and may not be effective against *T. pallidum*.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the Centers for Disease Control and Prevention (CDC) recommend a follow-up serological test 6-8 weeks after treatment to confirm the response to therapy and ensure that the infection has been cleared.

**Correct Answer:** B. Benzathine penicillin G.