Find out whether there is any grammatical error in below sentence. At the end of the year / every student who had done adequate work / was automatically promoted.

The correct answer is D. No error.

The sentence is grammatically correct. It is a simple sentence with three clauses:

• At
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  the
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  end of the year.
• Every student who had done adequate work.
• Was automatically promoted.

The first clause is a prepositional phrase that tells when the action happened. The second clause is a relative clause that tells which students were promoted. The third clause is the main clause that tells what happened to the students.

The sentence is clear and easy to understand. It is also concise and to the point. There is no need to change or add anything to the sentence.