**Core Concept**
The question is testing the student's knowledge of the preferred initial treatment for rheumatoid arthritis among the various disease-modifying anti-rheumatic drugs (DMARDs). Methotrexate is a commonly used DMARD that has been shown to effectively slow disease progression and improve symptoms in patients with rheumatoid arthritis.

**Why the Correct Answer is Right**
Methotrexate is considered the drug of first choice for rheumatoid arthritis due to its efficacy in reducing disease activity, slowing joint damage, and improving quality of life. It works by inhibiting the enzyme dihydrofolate reductase (DHFR), which is involved in the synthesis of tetrahydrofolate, a necessary precursor for DNA synthesis and repair. By blocking this enzyme, methotrexate reduces the proliferation of immune cells, thereby decreasing inflammation and joint damage. Additionally, methotrexate has a favorable safety profile and is relatively well-tolerated compared to other DMARDs.

**Why Each Wrong Option is Incorrect**
**Option B:** Gold compounds, such as auranofin, have been used in the past as DMARDs, but they are no longer considered a first-line treatment due to their toxicity and limited efficacy.
**Option C:** D-penicillamine is an immunosuppressive drug that has been used to treat rheumatoid arthritis, but it is associated with significant side effects, including rash, fever, and nephrotic syndrome, making it a less desirable choice as a first-line treatment.
**Option D:** Anakinra is an interleukin-1 receptor antagonist that is used to treat rheumatoid arthritis, but it is typically reserved for patients who have failed other DMARDs due to its high cost and limited efficacy.

**Clinical Pearl / High-Yield Fact**
When initiating treatment with methotrexate, it is essential to monitor liver function and complete blood counts regularly to minimize the risk of adverse effects.

**✓ Correct Answer: A. Methotrexate**