**Core Concept**
Herpangina and primary herpetic stomatitis are two distinct clinical entities caused by herpes simplex virus (HSV), but they exhibit different characteristics in terms of their presentation and oral cavity involvement. Herpangina typically affects the posterior part of the mouth, whereas primary herpetic stomatitis affects the anterior part.

**Why the Correct Answer is Right**
The correct answer highlights a key difference between herpangina and primary herpetic stomatitis. Herpangina is characterized by ulcers that are typically seen on the tonsillar pillars, which are located at the back of the throat, whereas primary herpetic stomatitis presents with ulcers on the anterior (front) faucial pillars. This difference in location is due to the distinct oral cavity involvement of each condition. Herpangina primarily affects the posterior part of the mouth, including the tonsillar pillars, whereas primary herpetic stomatitis affects the anterior part of the mouth.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because both herpangina and primary herpetic stomatitis can be preceded by prodromal symptoms such as fever, headache, and sore throat. The presence of prodromal symptoms is not a distinguishing feature between the two conditions.
**Option B:** This option is incorrect because both herpangina and primary herpetic stomatitis can be bilateral in nature. The condition can affect multiple sites in the mouth, including both sides of the oral cavity.
**Option D:** This option is incorrect because both herpangina and primary herpetic stomatitis are caused by the same virus, herpes simplex virus (HSV). The viral etiology is not a distinguishing feature between the two conditions.

**Clinical Pearl / High-Yield Fact**
A key clinical pearl to remember is that herpangina typically affects children and young adults, whereas primary herpetic stomatitis can occur in individuals of any age group. Additionally, herpangina is often associated with a more severe illness, including fever and lymphadenopathy, whereas primary herpetic stomatitis is generally a self-limiting condition.

**✓ Correct Answer: C. Ulcers relationship seen on the anterior faucial pillars**