**Core Concept**
Local anaesthetics are classified into two main groups: esters and amides. Ester local anaesthetics are metabolized by plasma cholinesterases, whereas amide local anaesthetics are metabolized by the liver.

**Why the Correct Answer is Right**
Ester local anaesthetics contain an ester linkage between the aromatic ring and the intermediate chain. Procaine is an example of an ester local anaesthetic, and it is metabolized by plasma cholinesterases to para-aminobenzoic acid (PABA). This metabolic pathway is unique to ester local anaesthetics and is an important consideration in their use.

**Why Each Wrong Option is Incorrect**
**Option A:** Lidocaine is an amide local anaesthetic, and it is not metabolized by plasma cholinesterases.
**Option B:** Prilocaine is also an amide local anaesthetic, and it is not an ester.
**Option C:** Bupivacaine is another amide local anaesthetic, and it is not an ester.

**Clinical Pearl / High-Yield Fact**
When using ester local anaesthetics, be aware of the potential for allergic reactions to para-aminobenzoic acid (PABA), which is a metabolite of these agents.

**Correct Answer: D. Procaine.