**Core Concept**
The question is testing the management of acute exacerbation of ulcerative colitis, a type of inflammatory bowel disease (IBD) characterized by chronic inflammation and ulceration of the colon mucosa. The choice of medication is based on the severity of the disease, the presence of complications, and the patient's response to previous treatments.

**Why the Correct Answer is Right**
Intravenous corticosteroids, such as methylprednisolone, are the first-line treatment for acute exacerbation of ulcerative colitis. They work by reducing inflammation and suppressing the immune system's abnormal response. Corticosteroids act by inhibiting the production of pro-inflammatory cytokines, such as TNF-alpha and IL-1 beta, and by inducing anti-inflammatory cytokines, such as IL-10. This leads to a decrease in the production of inflammatory mediators, such as prostaglandins and leukotrienes, which contribute to the symptoms of ulcerative colitis.

**Why Each Wrong Option is Incorrect**
**Option A:** Aminosalicylates, such as sulfasalazine, are effective for maintaining remission in ulcerative colitis but are not the first-line treatment for acute exacerbations.
**Option B:** Immunomodulators, such as azathioprine, are used for maintaining remission and as a steroid-sparing agent but are not the initial treatment for acute exacerbations.
**Option C:** Biologics, such as infliximab, are effective for inducing and maintaining remission in ulcerative colitis but are typically reserved for patients who have failed conventional therapy.

**Clinical Pearl / High-Yield Fact**
Intravenous corticosteroids should be initiated promptly in patients with acute exacerbation of ulcerative colitis, with a goal of inducing clinical remission within 7-10 days.

**Correct Answer: C. Methylprednisolone**