**Core Concept**
Primary syphilis is an infectious disease caused by the bacterium *Treponema pallidum*. The primary stage of syphilis is characterized by the formation of a chancre, a painless ulcer at the site of infection. The diagnosis and treatment of primary syphilis are critical to prevent the progression of the disease to its more severe forms.

**Why the Correct Answer is Right**
The recommended treatment for primary syphilis is a single dose of benzathine penicillin G, which is effective in eliminating the infection and preventing its transmission. This treatment is based on the principles of antimicrobial therapy, where the goal is to achieve a high concentration of the antibiotic at the site of infection to inhibit the growth and kill the causative microorganism. The use of benzathine penicillin G as the first-line treatment for syphilis is supported by its efficacy, safety, and simplicity of administration.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not represent the recommended treatment for primary syphilis.
**Option B:** This option is incorrect because it does not specify the type of penicillin used for the treatment of syphilis.
**Option C:** This option is incorrect because it does not represent the recommended dosage for the treatment of primary syphilis.

**Clinical Pearl / High-Yield Fact**
It is essential to note that primary syphilis can be effectively treated with a single dose of benzathine penicillin G, and patients should be followed up to ensure that the infection is cleared and that there are no signs of disease progression.

**Correct Answer:** D.