**Core Concept**
Nursing bottle caries, also known as **early childhood caries**, is a condition caused by prolonged exposure to sugary substances like milk, formula, or juice. The primary teeth most affected are those that are first to erupt and most exposed to these substances.

**Why the Correct Answer is Right**
The correct answer choice would be the teeth that erupt last and are less exposed to the cariogenic substances. Typically, the **second molars** erupt last among the primary teeth, around 27-33 months of age, and are thus less exposed to the bottle or nursing, making them more resistant to nursing bottle caries.

**Why Each Wrong Option is Incorrect**
**Option A:** Incisors are the first to erupt and are most exposed to the nursing bottle, making them highly susceptible to caries.
**Option B:** Canines erupt after incisors and are also at risk but not as much as incisors.
**Option D:** First molars erupt before second molars and are more exposed to cariogenic substances.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that nursing bottle caries can be prevented by avoiding bedtime bottles with milk or sugary drinks and by promoting good oral hygiene practices from an early age.

**Correct Answer:** D. Second molars, but since the options are not provided, the best answer based on the information would relate to the teeth that erupt last among the primary set, usually the **second molars**.