**Core Concept**
Cell cycle-specific anti-cancer drugs target specific phases of the cell cycle, which is the process by which a cell grows, replicates its DNA, and divides into two daughter cells. These drugs work by either inhibiting DNA synthesis or disrupting microtubule formation during specific phases of the cell cycle.

**Why the Correct Answer is Right**
The correct answer is a drug that targets the S phase of the cell cycle, where DNA synthesis occurs. This drug works by inhibiting the enzyme DNA polymerase, which is essential for DNA replication. By doing so, it prevents cancer cells from replicating their DNA and ultimately leads to cell death. The S phase is a critical phase of the cell cycle, and inhibiting it specifically targets rapidly dividing cancer cells.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it targets the M phase of the cell cycle, which is the phase of cell division. While it is an anti-cancer drug, it is not cell cycle-specific.
**Option B:** This option is incorrect because it targets the G1 phase of the cell cycle, which is the phase of cell growth. While it is an anti-cancer drug, it is not specific to the S phase.
**Option C:** This option is incorrect because it targets the G2 phase of the cell cycle, which is the phase of cell preparation for division. While it is an anti-cancer drug, it is not specific to the S phase.

**Clinical Pearl / High-Yield Fact**
Cell cycle-specific anti-cancer drugs are more effective against rapidly dividing cancer cells and are often used in combination with other therapies to enhance their effectiveness.

**Correct Answer: C. Cisplatin**