Parts of the following sentence have been given as options. Select the option that contains an error.
We were grateful for a book they gave us.

Correct option is D

Option (d) "a book" contains an error.
Explanation:
The sentence "We were grateful for a book they gave us." sounds unnatural because "a book" suggests any book in general, but when referring to a specific book that "they" gave, "the book" is the correct choice.
Correct sentence: We were grateful for the book they gave us.
Grammatical rule used:
When referring to a specific object (the book that "they" gave), the definite article "the" should be used instead of "a".
Explanation in Hindi:
यदि कोई वस्तु निर्दिष्ट (specific) हो, तो उसके लिए "the" का प्रयोग किया जाता है। चूंकि यह एक खास किताब की बात कर रहा है जो "they" ने दी थी, इसलिए सही वाक्य "the book" होगा, न कि "a book"।