**Core Concept**
Mesna is a medication used to prevent hemorrhagic cystitis, a side effect of certain chemotherapy drugs. It works by binding to and inactivating acrolein, a toxic metabolite produced by the breakdown of cyclophosphamide and ifosfamide.

**Why the Correct Answer is Right**
Mesna (sodium 2-sulfanylethanesulfonate) is unique among the options because it can be administered orally. This is due to its chemical structure, which allows it to be absorbed and metabolized effectively when taken by mouth. In contrast, the other options listed are either too toxic or too unstable to be given orally. For example, Actinomycin D (Dactinomycin) is a highly potent chemotherapeutic agent that is typically administered intravenously due to its high toxicity.

**Why Each Wrong Option is Incorrect**
**Option A:** Cytosine arabinoside (Ara-C) is a chemotherapeutic agent that is commonly administered intravenously or subcutaneously due to its poor oral bioavailability.
**Option B:** Actinomycin D (Dactinomycin) is a highly toxic chemotherapeutic agent that is typically administered intravenously due to its high toxicity.
**Option C:** Doxorubicin is a chemotherapeutic agent that is commonly administered intravenously due to its poor oral bioavailability and potential for cardiotoxicity when taken orally.

**Clinical Pearl / High-Yield Fact**
When administering chemotherapy, it is essential to consider the route of administration to maximize bioavailability and minimize toxicity. Mesna's oral bioavailability makes it a convenient option for preventing hemorrhagic cystitis in patients receiving cyclophosphamide or ifosfamide.

**✓ Correct Answer: D. Mesna**