A :The regular sequences of a cell cycle is `G_(1),S,G_(2),M` and C
R: Replication of DNA occurs during S phase.

Options

A. If both As and R are correct and R is correct explanation of As
B. If both As and R are correct but R is not correct explanation of As
C. If As is correct, R is wrong
D. If both As and R are wrong.

Answer

To solve the question, we need to analyze both the assertion (A) and the reason (R) provided.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that the regular sequence of the cell cycle is G1, S, G2, M, and C.
- The cell cycle consists of several phases:
- **G1 phase** (Gap 1): The cell grows and synthesizes proteins necessary for DNA replication.
- **S phase** (Synthesis): DNA replication occurs during this phase.
- **G2 phase** (Gap 2): The cell continues to grow and prepares for mitosis.
- **M phase** (Mitosis): The cell divides.
- **C phase** (Cytokinesis): The cytoplasm divides, resulting in two daughter cells.

2. **Understanding the Reason (R)**:
- The reason states that replication of DNA occurs during the S phase.
- This is a well-established fact in cell biology. During the S phase, each chromosome is replicated to produce two sister chromatids.

3. **Evaluating the Truth of A and R**:
- Both statements are true:
- The sequence of the cell cycle as stated in the assertion is correct.
- The reason correctly identifies that DNA replication occurs during the S phase.

4. **Relationship Between A and R**:
- The reason (R) explains the assertion (A). The assertion describes the phases of the cell cycle, and the reason provides a specific detail about one of those phases (S phase) regarding DNA replication.

5. **Conclusion**:
- Since both the assertion and reason are true, and the reason explains the assertion, the correct option is that both A and R are true, and R explains A.

### Final Answer:
Both the assertion and reason are true, and the reason explains the assertion.

---