## Core Concept
Multiple sclerosis (MS) is a chronic autoimmune disease characterized by demyelination, inflammation, and axonal damage in the central nervous system (CNS). The relapsing-remitting form of MS (RRMS) is the most common type, marked by episodes of neurological symptoms (relapses) followed by periods of partial or complete recovery. Disease-modifying therapies (DMTs) are crucial in managing RRMS.

## Why the Correct Answer is Right
The correct answer, **Dimethyl fumarate**, is a DMT that has been shown to be effective in reducing relapse rates, delaying disability progression, and decreasing the formation of new lesions in the CNS as observed in MRI scans. It is an oral medication that acts by modulating the immune system, although its exact mechanism of action in MS is not fully understood. Dimethyl fumarate has become a preferred option due to its efficacy, oral administration, and relatively favorable side effect profile compared to other DMTs.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because, although some DMTs are administered via injection or infusion, Dimethyl fumarate is specifically noted for its oral formulation, making it more convenient for patients.
- **Option B:** This option is incorrect because, while other medications like interferon beta-1a are used in MS treatment, Dimethyl fumarate has demonstrated a more favorable balance of efficacy and safety in many patients.
- **Option C:** This option is incorrect as it might refer to another DMT; however, Dimethyl fumarate stands out for its efficacy in RRMS.
- **Option D:** This option is incorrect because, although Glatiramer acetate is another first-line treatment for RRMS, Dimethyl fumarate has been favored for its oral administration and comparable or superior efficacy in certain aspects.

## Clinical Pearl / High-Yield Fact
A key point to remember is that Dimethyl fumarate, before initiation, requires patients to have their complete blood count (CBC) checked due to the risk of lymphopenia, a potential side effect of the medication. Monitoring for signs of progressive multifocal leukoencephalopathy (PML), a rare but serious brain infection, is also crucial.

## Correct Answer Line
**Correct Answer: C. Dimethyl fumarate.**