**Core Concept**
The underlying principle being tested is the development and eruption of teeth in the human mouth, specifically focusing on the mixed dentition stage. At the age of 12, children typically have a combination of primary and permanent teeth. The **dental formula** for permanent teeth is crucial for understanding the correct answer.

**Why the Correct Answer is Right**
By the age of 12, most children have started to lose their primary teeth, which are gradually replaced by permanent teeth. The first permanent molars, also known as the "six-year molars," erupt around the age of 6, and by 12, most of the incisors, canines, and premolars have also erupted. Understanding the sequence and timing of tooth eruption is key to determining the total number of teeth at this age.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it underestimates the number of teeth that have erupted by the age of 12.
**Option B:** This option might seem plausible but does not accurately reflect the typical dental development at this age.
**Option D:** This option overestimates the number of teeth, as not all permanent teeth have erupted by the age of 12.

**Clinical Pearl / High-Yield Fact**
A crucial point to remember is that the total number of teeth in the mouth at any given time can vary due to the gradual replacement of primary teeth with permanent ones. Knowing the typical sequence and timing of tooth eruption is vital for dental assessments and treatments.

**Correct Answer:** Correct Answer: C. 28.