**Core Concept**
The structural classification of beta-lactamases is a system used to categorize these enzymes based on their three-dimensional structure. This classification helps in understanding the mechanism of action and the substrate specificity of different beta-lactamases.

**Why the Correct Answer is Right**
The structural classification of beta-lactamases was given by Ambler, who categorized them into four classes (A, B, C, and D) based on the amino acid sequence and the conserved active site residues. Class A beta-lactamases are the most common and are typically found in Gram-negative bacteria, while Class C beta-lactamases are often associated with Gram-positive bacteria. Class B beta-lactamases are metallo-beta-lactamases that require a metal ion for catalytic activity, and Class D beta-lactamases are also known as oxacillinases.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Ambler did not propose this classification system.
**Option B:** This option is incorrect because Ambler is credited with the structural classification of beta-lactamases, not this person.
**Option C:** This option is incorrect because Ambler's classification system is based on the amino acid sequence and conserved active site residues, not just the enzyme's function.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the structural classification of beta-lactamases helps in predicting the enzyme's substrate specificity and the potential for resistance development. This knowledge is crucial for selecting the appropriate antibiotic therapy and monitoring for resistance.

**Correct Answer: A. Ambler**