**Core Concept**
The treatment of abdominal sepsis involves the administration of broad-spectrum antibiotics to cover a wide range of potential pathogens. The combination of intravenous ampicillin and gentamicin is a common empirical treatment regimen for this condition.

**Why the Correct Answer is Right**
The combination of ampicillin and gentamicin is chosen for its synergistic effect against a broad range of Gram-positive and Gram-negative bacteria. Ampicillin is a beta-lactam antibiotic that inhibits cell wall synthesis, while gentamicin is an aminoglycoside antibiotic that binds to the 30S subunit of the bacterial ribosome, inhibiting protein synthesis. This synergistic effect is particularly effective against bacteria such as *Escherichia coli*, *Klebsiella pneumoniae*, and *Bacteroides fragilis*, which are commonly implicated in abdominal sepsis.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as it does not specify the combination of antibiotics used. While ampicillin and gentamicin are effective against Gram-positive and Gram-negative bacteria, respectively, their combination is not the only option for treating abdominal sepsis.
* **Option B:** This option is incorrect as it suggests using a single antibiotic, which may not be effective against a polymicrobial infection such as abdominal sepsis.
* **Option D:** This option is incorrect as it suggests using a different class of antibiotics, which may not be as effective against the range of pathogens implicated in abdominal sepsis.

**Clinical Pearl / High-Yield Fact**
In the treatment of abdominal sepsis, the choice of antibiotics should be guided by the severity of the infection, the patient's underlying health status, and the results of any available cultures. A combination of antibiotics with synergistic effects, such as ampicillin and gentamicin, is often used as an empirical treatment regimen.

**Correct Answer:** C.