In this sentence completion question on English usage, fill in the blank in the sentence "Even if two horses may look _____, they may not be of the same age" with the most appropriate word or phrase from the given options.

Introduction / Context:
Fill in the blank questions test your sense of natural English collocations and your ability to choose the most appropriate word so that the sentence becomes meaningful and grammatically correct. Here, the sentence compares two horses that look similar but may differ in age. You need a word that completes the comparison in a way that English speakers commonly use.

Given Data / Assumptions:
• The sentence is: "Even if two horses may look _____, they may not be of the same age." • The options are "comparable", "alike", "on par", and "only same". • The context is visual similarity versus actual age.

Concept / Approach:
When we talk about two things that look similar in appearance, a very natural and common expression in English is "look alike". The word "alike" is used after verbs like "look" or "seem" to express similarity. The other options are not idiomatically suitable in this structure. The approach is to mentally complete the sentence with each option and check which sounds natural and preserves the intended meaning: similar outward appearance but possibly different real characteristics.

Step-by-Step Solution:
Step 1: Insert "comparable": "Even if two horses may look comparable, they may not be of the same age." Although the meaning is understandable, the collocation "look comparable" is not the most natural choice; we usually say things are comparable in terms of price, value, or quality rather than appearance. Step 2: Insert "alike": "Even if two horses may look alike, they may not be of the same age." This is a common and idiomatic construction when referring to similar appearance. Step 3: Insert "on par": "Even if two horses may look on par..." This phrase is awkward because "on par" is typically used with "be" rather than "look", and it refers more to equal quality or level than to visual similarity. Step 4: Insert "only same": "Even if two horses may look only same..." This is not correct English; the phrase is ungrammatical and unnatural. Step 5: Conclude that "alike" is the best and correct fit for the context and structure.

Verification / Alternative check:
You can test the choice by trying similar sentences: "Even if two brothers look alike, their personalities may be different." This sentence is perfectly natural and very common in English. Replacing "alike" with any of the other options makes the sentence sound forced or incorrect. Native speakers almost always use "look alike" when talking about similar appearance of people or animals.

Why Other Options Are Wrong:
"Comparable" usually pairs with "be" or "remain" rather than "look" and focuses on equality in value, usefulness, or performance rather than purely visual similarity. "On par" is a phrase used to mean equivalent or equal in quality or status and again typically follows linking verbs, not "look", and is not used for visual resemblance. "Only same" is grammatically wrong; we would say "the same" or "only similar", but the given combination does not form a correct phrase.

Common Pitfalls:
Learners often overvalue more sophisticated sounding words like "comparable" and may pick them even when a simple, everyday word is a better fit. Exam setters deliberately include such distractors. The key is to prioritise natural usage and idiomatic combinations. Regular reading of good English text builds an ear for what sounds right and helps you choose the most suitable option in sentence completion tasks.

Final Answer:
The correct word to fill the blank is alike.