**Core Concept**
Penicillinase-resistant penicillins are a class of antibiotics that have been designed to withstand the action of beta-lactamase enzymes produced by certain bacteria, such as Staphylococcus aureus. These enzymes break down the beta-lactam ring of penicillins, rendering them ineffective. By modifying the beta-lactam ring or adding other functional groups, penicillinase-resistant penicillins can evade this enzymatic degradation.

**Why the Correct Answer is Right**
Penicillinase-resistant penicillins, such as methicillin and oxacillin, contain a modified beta-lactam ring that is resistant to cleavage by beta-lactamases. This modification prevents the enzyme from breaking the beta-lactam ring, thereby maintaining the antibiotic's efficacy. Additionally, these antibiotics often have a bulky side chain that blocks access to the beta-lactam ring, further inhibiting the action of beta-lactamases.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not specify a particular type of penicillin that is resistant to penicillinase.
**Option B:** This option is incorrect as it does not accurately describe a penicillinase-resistant penicillin.
**Option C:** This option is incorrect as it is a different class of antibiotics altogether.

**Clinical Pearl / High-Yield Fact**
When choosing an antibiotic to treat a bacterial infection, it is essential to consider the local resistance patterns and the specific characteristics of the pathogen. Penicillinase-resistant penicillins are often used to treat infections caused by Staphylococcus aureus and other beta-lactamase-producing bacteria.

**Correct Answer: C. Methicillin.**