**Core Concept**
The patient's presentation with abdominal pain, fever, and a mass involving the sigmoid colon is suggestive of diverticulitis, a common cause of lower gastrointestinal tract obstruction. Diverticulitis is characterized by inflammation of the diverticula, which are outpouchings of the colonic wall.

**Why the Correct Answer is Right**
The initial treatment of diverticulitis typically involves broad-spectrum antibiotics to cover both aerobic and anaerobic bacteria, which are commonly involved in this condition. The choice of antibiotics should include coverage for both gram-positive and gram-negative bacteria, as well as anaerobes. The goal of initial treatment is to control the infection and prevent complications.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not address the need for antibiotic coverage. While bowel rest may be a part of the treatment plan, it is not the initial treatment.

**Option B:** This option is incorrect because it does not provide adequate coverage for anaerobic bacteria, which are commonly involved in diverticulitis. While metronidazole has some activity against anaerobes, it is often used in combination with other antibiotics for optimal coverage.

**Option C:** This option is incorrect because it does not address the need for broad-spectrum antibiotic coverage. While ciprofloxacin has some activity against gram-negative bacteria, it does not provide adequate coverage for anaerobes or gram-positive bacteria.

**Clinical Pearl / High-Yield Fact**
The Hinchey classification is a useful tool for predicting the likelihood of complications in patients with diverticulitis. It categorizes patients into four grades based on the presence and extent of complications, such as abscess formation or perforation.

**Correct Answer: B. Ciprofloxacin and metronidazole.**