**Core Concept**
Sulfonamides are a class of antimicrobials that inhibit bacterial growth by competitively inhibiting the action of para-aminobenzoic acid (PABA), a precursor to folic acid. They work by disrupting the bacterial synthesis of tetrahydrofolate, an essential cofactor for DNA synthesis and repair.

**Why the Correct Answer is Right**
The correct answer is related to the mechanism of action of sulfonamides. Sulfonamides are bacteriostatic at low concentrations and bactericidal at high concentrations. They inhibit the activity of dihydropteroate synthetase, an enzyme crucial for the synthesis of tetrahydrofolate. This disrupts the bacterial production of thymidylate, a necessary component of DNA.

**Why Each Wrong Option is Incorrect**
**Option A:** This statement is true as sulfonamides are effective against a wide range of gram-positive and gram-negative bacteria. However, it's not the correct answer as we are looking for a statement that is NOT true.

**Option B:** This statement is true as sulfonamides are often used in combination with other antimicrobials to enhance their effectiveness and reduce the likelihood of resistance.

**Option C:** This statement is false as sulfonamides are generally not effective against viruses and are therefore not used to treat viral infections.

**Clinical Pearl / High-Yield Fact**
Sulfonamides can cause a range of adverse effects, including hypersensitivity reactions, hematologic toxicity, and crystalluria. It's essential to monitor patients for signs of these complications, particularly when using high-dose or long-term therapy.

**Correct Answer: C. Sulfonamides are generally not effective against viruses.**