Select the synonym (nearest in meaning) of the word "bristle".

Introduction / Context:
This question asks for a synonym of the word bristle. Bristle can function both as a noun and as a verb. As a noun, it refers to a short, stiff hair or fibre, like those on a brush or an animal hide. As a verb, it can mean to react angrily or defensively. Given the options, the exam clearly focuses on the concrete, noun meaning of bristle rather than the emotional reaction sense.

Given Data / Assumptions:

• Bristle (noun) means a short, stiff hair, often on a brush, an animal, or a person chin.
• Thorn is a sharp, pointed growth on the stem of a plant, especially a rose or similar bush.
• Tranquil means calm and peaceful.
• Friction is rubbing of one surface against another or conflict between people.
• Sleek means smooth and shiny, often referring to hair or fur.

Concept / Approach:
Among the given options, the only word that refers to a small, pointed, stiff object is thorn. While a bristle is not exactly the same as a thorn, both share the idea of a small, stiff projection. The other words belong to completely different semantic fields: tranquillity, conflict, and smoothness. Since exam synonyms are often approximate rather than perfect, thorn is the closest match available here.

Step-by-Step Solution:
Step 1: Decide which sense of bristle is likely being tested. Because none of the options relates to anger or defensiveness, the physical noun sense is more relevant.Step 2: Compare bristle as a short stiff hair with each option.Step 3: Recognise that thorn, although from plants, is also a small, sharp, stiff projection and is the nearest in physical imagery.Step 4: Check tranquil, friction, and sleek; none of these describes a small, stiff object and they do not match the noun sense of bristle.Step 5: Conclude that thorn is the best available synonym in this list.

Verification / Alternative check:
Consider descriptive sentences. A brush with stiff bristles and The stem was covered in sharp thorns both paint pictures of small, stiff projections that can scratch or irritate the skin. The words are not identical but share overlapping imagery. On the other hand, bristle does not relate directly to calmness (tranquil), conflict (friction), or smoothness (sleek). If we tried to replace bristle with any of these in a sentence like The pig coarse bristles stood up, the sentence would become nonsense.

Why Other Options Are Wrong:
Tranquil is an adjective describing a peaceful state, often of places or moods. Friction is a noun of motion and social conflict, not a physical protrusion. Sleek describes something smooth and well groomed, usually the opposite of bristly. None of these words shares the core physical meaning associated with bristle as a noun.

Common Pitfalls:
Because bristle also means to react angrily or defensively (as a verb), some students may search for an emotional or conflict related synonym and be tempted by friction. However, the verb to bristle and the noun friction do not align exactly, and no option fully matches that emotional sense here. The safer strategy is to consider the more basic, noun meaning and choose the closest concrete object, which is thorn.

Final Answer:
The best available synonym of bristle among the given options is thorn, so option A is correct.