**Core Concept**
The question is testing the ability to identify a characteristic feature of a snake species, specifically the size of the infralabial scales. Infralabial scales are the scales located below the chin in snakes, and their size and arrangement can be used to identify different species.

**Why the Correct Answer is Right**
The size of the infralabial scales can be an important characteristic in identifying snake species. In the case of the 4th infralabial being larger than others on either side, it may indicate the presence of a particular species that has this distinctive feature. This characteristic can be used in conjunction with other morphological features to make a positive identification.

**Why Each Wrong Option is Incorrect**
**Option B:** This option is incorrect because it is not a valid characteristic for identifying snake species. The size of the infralabial scales is a specific feature that can be used to identify certain species, but it is not a general characteristic that applies to all snakes.
**Option C:** This option is incorrect because it is not a specific or reliable characteristic for identifying snake species. While some snakes may have larger infralabial scales, this is not a distinctive feature that can be used to make a positive identification.
**Option D:** This option is incorrect because it is not a valid or reliable characteristic for identifying snake species. The size of the infralabial scales can vary among individuals of the same species, and it is not a consistent feature that can be used to make a positive identification.

**Clinical Pearl / High-Yield Fact**
When identifying snake species, it is often necessary to examine multiple characteristics, including the size and arrangement of the infralabial scales. This requires a thorough understanding of the morphology of different snake species and the ability to recognize distinctive features.

**Correct Answer:** C. Cobra.