Read each sentence to find out whether there is any grammatical or idiomatic error in it. The error, if any, will be in one part of the sentence. The corresponding letter of that part is the answer. If the given sentence is grammatically and contextually correct, then choose option “No error” as answer. (Ignore errors of punctuation, if any.)

I haven't saw (A) / such a beautiful (B) / sunset in my (C) / entire life. (D) / No error (E)

Correct option is A

The grammatical error is in part (A) of the sentence. The past tense of the verb "see" should be "seen" instead of "saw" when used with the auxiliary verb "have." The correct past participle form of the verb "see" is "seen," so it should be "I haven't seen." No other parts of the sentence contain an error with respect to the larger context of the sentence. The correct sentence should be:
I haven't seen (A) / such a beautiful (B)/ sunset in my (C) / entire life. (D)
Therefore, the answer is (a) A.