The correct answer is: D. No error.
The sentence “The reason why he was rejected
was because he was too young” is grammatically correct. The word “because” is used to introduce a reason or cause. In this sentence, it is used to explain why the person was rejected. The sentence is also clear and concise, and it conveys the intended meaning effectively.The other options are incorrect because they contain grammatical errors. Option A, “The reason why,” is a dangling modifier. A dangling modifier is a word or phrase that does not clearly modify the word or phrase it is intended to modify. In this case, the word “why” does not clearly modify any word in the sentence. Option B, “he was rejected,” is a fragment. A fragment is a group of words that does not express a complete thought. In this case, the word “he” is not followed by a verb, so the sentence is incomplete. Option C, “was because he was too young,” is a run-on sentence. A run-on sentence is two or more independent clauses that are not joined by a coordinating conjunction or a semicolon. In this case, the two clauses “he was rejected” and “he was too young” are not joined by any punctuation, so the sentence is grammatically incorrect.