**Core Concept:**

The question tests our understanding of nucleotides, which are the building blocks of DNA and RNA. In both DNA and RNA, nucleotides are composed of three parts: a sugar (deoxyribose or ribose), a phosphate group, and a nitrogenous base. There are four types of nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T) in DNA, and adenine (A), guanine (G), cytosine (C), and uracil (U) in RNA. The question asks about the equal number of nucleotide bases between a specific pair of nucleotides.

**Why the Correct Answer is Right:**

The correct answer is **D.** In both DNA and RNA, the pairs of nitrogenous bases complement each other, which is essential for the stability and function of these molecules. These complementary base pairs are:

1. Adenine (A) pairs with Thymine (T) in DNA, and with Uracil (U) in RNA.
2. Guanine (G) pairs with Cytosine (C) in DNA, and with Adenine (A) in RNA.

**Why Each Wrong Option is Incorrect:**

A) Option A (A with T) is incorrect because A pairs with T, not A.
B) Option B (G with C) is incorrect because G pairs with C, not G.
C) Option C (A with U) is incorrect because A pairs with T, not U.

**Clinical Pearl / High-Yield Fact:**

The concept of complementary base pairing helps us understand the genetic information storage and transmission in cells. This principle is crucial for understanding molecular biology and genetics, as well as various genetic disorders and treatments.

**Correct Answer: D.** Nucleotides in DNA and RNA pair in a complementary manner to ensure accurate genetic information storage and transmission.