## Core Concept
The development of primary teeth, also known as deciduous or baby teeth, involves several stages including formation, eruption, and root completion. Understanding the timeline of these stages is crucial for pediatric dentistry and general knowledge of human dentition development.

## Why the Correct Answer is Right
The correct answer states that the time taken for primary tooth root completion after eruption is approximately 1-1.5 years. This duration is consistent with the general developmental timeline of primary teeth. After a primary tooth erupts, the root continues to develop and usually reaches completion within a year or so. This process is essential for the tooth's stability and function in the oral cavity.

## Why Each Wrong Option is Incorrect
- **Option A:** This option suggests a significantly shorter duration, which underestimates the time required for root completion.
- **Option B:** This option implies a longer duration than generally accepted for primary teeth root completion.
- **Option D:** This option provides a range that does not accurately reflect the typical timeline for root completion of primary teeth after eruption.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the roots of primary teeth are completely formed within 1-1.5 years after eruption. This fact is crucial for dental professionals, especially when planning treatments or assessing the development of primary dentition in children.

## Correct Answer: C. 1-1.5 years.