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.)

She asked me (A) / if I can help her (B) / move the furniture (C) / this weekend. (D) / No Error (E)

Correct option is B

The grammatical error is in part (B) of the sentence. The verb "can" should be changed to "could" because the sentence is in the past tense and requires the past form of the verb. No other parts of the sentence contain an error with respect to the larger context of the sentence. The correct sentence should be:
She asked me (A) / if I could help her (B) / move the furniture (C) / this weekend. (D)
Therefore, the answer is (b) B.