**Core Concept**
Smooth surface caries refers to the progression of dental caries on the smooth surfaces of teeth, primarily affecting the enamel and dentin. This type of caries is characterized by the formation of cone-shaped lesions, which are a result of the acid produced by oral bacteria dissolving the mineral content of the tooth structure.

**Why the Correct Answer is Right**
The alignment of these cone-shaped lesions in enamel and dentin is a result of the acid dissolution process, which affects the enamel and dentin in a predictable pattern. The acid produced by oral bacteria, primarily from Streptococcus mutans, dissolves the minerals in the enamel, creating a cone-shaped lesion. As the caries progresses, the acid dissolves the dentin, also creating a cone-shaped lesion. The alignment of these lesions is due to the fact that the acid dissolution process is more rapid in the enamel than in the dentin.

* The acid dissolution process affects the enamel first, creating a cone-shaped lesion that is more rapid in the surface enamel.
* The dentin lesion is slower to develop and is more irregular in shape.
* The alignment of the cone-shaped lesions in enamel and dentin is affected by the rate of acid dissolution and the mineral content of the tooth structure.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately describe the alignment of cone-shaped lesions in enamel and dentin.
* **Option B:** This option is incorrect because it does not accurately describe the alignment of cone-shaped lesions in enamel and dentin.
* **Option D:** This option is incorrect because it does not accurately describe the alignment of cone-shaped lesions in enamel and dentin.

**Clinical Pearl / High-Yield Fact**
The alignment of cone-shaped lesions in enamel and dentin is a key characteristic of smooth surface caries, and it is essential to recognize this pattern in order to diagnose and treat this condition effectively.

**Correct Answer: C. Perpendicular alignment.**