In this English grammar question on preference expressions, identify which part of the sentence is incorrect in: "I prefer this book than that one."

Introduction / Context:
This question examines the correct use of the verb "prefer" in English, particularly the preposition that should follow it when two alternatives are compared. The sentence given is "I prefer this book than that one." Such structures are frequently tested in competitive exams because many learners mistakenly combine "prefer" with "than", copying the pattern from comparative adjectives like "better than". Understanding the correct pattern "prefer A to B" is essential for accurate speaking and writing.

Given Data / Assumptions:

• The full sentence is: "I prefer this book than that one."
• Segment (a) is "I prefer".
• Segment (b) is "this book".
• Segment (c) is "than that one."
• Segment (d) is "No error".
• The question expects standard British or Indian English usage of the verb "prefer".

Concept / Approach:
The verb "prefer" is used with the preposition "to" when directly comparing two nouns or noun phrases. The standard pattern is "prefer A to B". For example, "I prefer tea to coffee" and "They prefer staying at home to going out." Using "than" after "prefer" is considered incorrect in formal English, although it is heard in colloquial speech. Therefore, the phrase "than that one" after "prefer this book" is wrong and should be replaced by "to that one". The other parts of the sentence are structurally sound.

Step-by-Step Solution:
Step 1: Isolate the structure of preference: "I prefer this book than that one." Step 2: Recall the correct pattern: "prefer A to B", where A and B are things being compared. Step 3: Identify A as "this book" and B as "that one". Step 4: Notice that the sentence uses "than" instead of "to" between the two compared items. Step 5: Recognize that the grammatically correct form is "I prefer this book to that one." Step 6: Conclude that segment (c) "than that one." contains the error, while segments (a) and (b) are fine.

Verification / Alternative check:
To verify, compare with other correct examples. Sentences like "She prefers coffee to tea", "We prefer buses to trains", and "They prefer reading to watching television" all use "to" after "prefer". If we substitute "than" in these sentences, they sound unnatural and are not accepted in standard grammar references. Applying the same logic, "I prefer this book to that one" is the only correct version. This confirms that the preposition in segment (c) is the problem.

Why Other Options Are Wrong:
Option (a) "I prefer" is a correct way to express personal choice or liking. Option (b) "this book" correctly acts as the first item in the comparison. Option (d) "No error" is not suitable because we have identified a clear mistake in segment (c).

Common Pitfalls:
Learners often confuse the structures "prefer A to B" and "like A better than B". Because "better than" uses "than", they sometimes incorrectly attach "than" to "prefer" as well. It is important to remember that "prefer" has its own fixed pattern. A helpful memory trick is to pair "prefer" with "to" and "better" with "than". Regular practice with example sentences helps solidify this distinction and avoid repeated errors in speaking and writing.

Final Answer:
The error lies in option (c) "than that one." It should be "to that one." Therefore, the correct answer is "than that one.".