Cell would normally proceed to mitosis without interruption

Options

A. once it has entered the S phase
B. once it has entered the `G_(2)` phase
C. at any time during cell division activity
D. none of these

Explanation

**Step-by-Step Solution:**

1. **Understanding the Cell Cycle**: The cell cycle consists of interphase and mitotic phase. Interphase is further divided into three stages: G1 (Gap 1), S (Synthesis), and G2 (Gap 2).

2. **Identifying the Checkpoints**: During the cell cycle, there are checkpoints that regulate the progression of the cell. The first checkpoint occurs between G1 and S phase, known as the G1 checkpoint.

3. **G1 Phase and G0 Phase**: In the G1 phase, the cell can either proceed to the S phase or enter a resting state known as G0 phase. If it enters G0, it will not divide.

4. **Crossing the G1 Checkpoint**: If the cell successfully passes the G1 checkpoint, it will move into the S phase. This is a critical transition point.

5. **Entering the S Phase**: Once the cell enters the S phase, it begins DNA replication. At this stage, the cell is committed to completing the cycle and will proceed to mitosis without interruption.

6. **Conclusion**: Therefore, the correct answer to the question is that the cell would normally proceed to mitosis without interruption once it has entered the S phase.

**Final Answer**: The correct option is **once it has entered the S phase**.

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