Uracil occurs in DNA and not in RNA.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Statement**: The statement claims that uracil occurs in DNA and not in RNA. We need to evaluate this statement for its accuracy.

2. **Identifying the Nucleobases**: In nucleic acids, DNA and RNA are composed of different nitrogenous bases. DNA contains adenine (A), thymine (T), guanine (G), and cytosine (C). RNA, on the other hand, contains adenine (A), uracil (U), guanine (G), and cytosine (C).

3. **Comparing Uracil and Thymine**: Uracil and thymine are both pyrimidine bases. The key difference between them is that thymine has a methyl group (-CH3) attached to its structure, while uracil does not. This structural difference is crucial in distinguishing the two bases.

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