In RNA, thymine is replaced by

Options

A. adenine
B. guanine
C. cytosine
D. uracil

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks what replaces thymine in RNA. In DNA, the four bases are adenine (A), thymine (T), cytosine (C), and guanine (G). In RNA, one of these bases is different.

2. **Identifying the Base in RNA**: In RNA, thymine (T) is replaced by uracil (U). This is a fundamental difference between DNA and RNA. While DNA contains thymine, RNA contains uracil instead.

3. **Transcription Process**: The process of synthesizing RNA from DNA is called transcription. During transcription, the DNA template is read, and complementary RNA bases are formed. For example, where there is an adenine (A) in DNA, uracil (U) will be placed in RNA instead of thymine.

4. **Base Pairing**: In DNA, adenine pairs with thymine (A-T), while in RNA, adenine pairs with uracil (A-U). The other base pairings remain the same: cytosine pairs with guanine (C-G) in both DNA and RNA.

5. **Conclusion**: Therefore, the answer to the question is that in RNA, thymine is replaced by uracil.

**Final Answer**: In RNA, thymine is replaced by uracil.

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