## **Core Concept**
DNA (Deoxyribonucleic acid) base pairing is a fundamental concept in molecular biology. The base pairing rules in DNA are as follows: **Adenine (A)** pairs with **Thymine (T)**, and **Cytosine (C)** pairs with **Guanine (G)**. This base pairing is crucial for the replication and transcription of genetic material.

## **Why the Correct Answer is Right**
Cytosine (C) is paired with Guanine (G) in DNA through three hydrogen bonds. This specific pairing is essential for the stability and function of the DNA double helix. The pairing between C and G is as follows: Cytosine, which is a pyrimidine, forms hydrogen bonds with Guanine, a purine, through its amino group and keto group.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Adenine (A) is incorrect because it pairs with Thymine (T), not Cytosine (C).
- **Option B:** Thymine (T) is incorrect because it pairs with Adenine (A), not Cytosine (C).
- **Option D:** Uracil (U) is incorrect because it is found in RNA, where it pairs with Adenine (A), replacing Thymine. In DNA, Uracil is not present; instead, Thymine takes its place.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is the base pairing rules in DNA and RNA: **DNA - A-T, G-C** and **RNA - A-U, G-C**. This difference is critical for understanding molecular biology techniques and the central dogma of molecular biology.

## **Correct Answer:** . Guanine