## **Core Concept**
The question tests the pharmacokinetic property of a specific drug, focusing on its excretion and potential side effects. The drug in question is primarily excreted unchanged in the urine and has a low solubility in urine, which necessitates adequate hydration to prevent renal complications.

## **Why the Correct Answer is Right**
The correct answer, **C. Methotrexate**, fits the description provided. Methotrexate is a chemotherapeutic agent and immune system modulator that is primarily excreted unchanged in the urine. Its low solubility in urine can lead to crystalluria and nephrotoxicity if the patient is not well-hydrated. This characteristic necessitates careful management to prevent renal complications.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is not specified, but generally, drugs not matching the description of high urinary excretion in intact form or not known for nephrotoxicity risk due to low urinary solubility would be incorrect.
- **Option B:** Similarly, without specifics, any drug not primarily excreted unchanged in the urine or not known for the risk of nephrotoxicity due to low solubility would not fit.
- **Option D:** This option also lacks specifics, but clearly, any drug not meeting the criteria of being excreted more than 90% in intact form in the urine and not posing a significant risk of nephrotoxicity due to low urinary solubility would be incorrect.

## **Clinical Pearl / High-Yield Fact**
A critical point to remember is that for drugs like methotrexate, **adequate hydration and alkalinization of the urine** can help prevent nephrotoxicity by reducing the risk of crystalluria. This is a high-yield fact for exams and clinical practice, especially in oncology and rheumatology.

## **Correct Answer:** . **C. Methotrexate**