Choose the option that best expresses the meaning of the idiom "as fit as a fiddle" in everyday English usage.

Introduction / Context:
Idioms often use colourful images to express simple ideas. The phrase as fit as a fiddle is a classic English idiom that appears in conversations, health advice, and exam questions. Although it mentions a musical instrument, it has nothing to do with music. Instead, it is about physical health and energy. This question asks you to select the option that best captures the meaning of this idiom in everyday usage.

Given Data / Assumptions:

• The idiom is as fit as a fiddle.
• We assume standard British and international English usage.
• The options present different emotional or physical states.
• Only one option refers directly to being in excellent health.

Concept / Approach:
As fit as a fiddle means extremely healthy and in very good physical condition. Historically, fiddles (violins) were associated with being well tuned and functioning perfectly. By comparing a person to a well tuned instrument, the idiom suggests that the body is in excellent working order. It does not describe aggression, discomfort, or selfishness; it is a positive expression often used when someone has recovered from illness or has always maintained good health.

Step-by-Step Solution:
Step 1: Recall that the word fit in this idiom refers to physical fitness, not anger or suitability. Step 2: Remember that as fit as a fiddle is spoken as praise, usually when someone is strong and energetic. Step 3: Examine the options and choose the one that clearly states strong, healthy and in good physical condition. Step 4: Rule out options that refer to aggression, discomfort, or selfish personality traits, because they do not match the positive health related meaning. Step 5: Confirm that Option D aligns directly with the idiom's standard interpretation.

Verification / Alternative check:
Consider sample sentences: After months of rest and exercise, she is now as fit as a fiddle. Here, the idea is that she is fully recovered and in excellent shape. Another example: Despite his age, he is as fit as a fiddle and walks several kilometres every day. In both cases, replacing as fit as a fiddle with strong, healthy and in good physical condition preserves the full meaning. In contrast, substituting aggressive, uncomfortable, or selfish friend would make the sentences absurd, confirming that those options are incorrect.

Why Other Options Are Wrong:
Very aggressive and quick to fight: This is wrong because the idiom does not involve anger or a fighting spirit; it is purely about health and fitness.
Uncomfortable and restless: This is wrong because it describes a negative physical or emotional state, opposite to the comfort and vitality implied by the idiom.
A selfish and unreliable friend: This is wrong because it refers to personality and behaviour in relationships, which is unrelated to the body's fitness.

Common Pitfalls:
Some learners misunderstand fit as a reference to being ready to fight or being suitable for something, leading them to pick aggressive options. Others become distracted by the word fiddle and think about music rather than health. To avoid confusion, remember that in health related idioms, fit usually refers to physical well being. Whenever you see as fit as a fiddle in a sentence, think strong and healthy, not angry or musical.

Final Answer:
The idiom as fit as a fiddle means Strong, healthy and in good physical condition.