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 “No error” as the correct answer. (Ignore errors of punctuation, if any.)

She has been (A) / working very hardly (B) / to complete her project (C) / before the deadline. (D)

Correct option is B

The sentence has a grammatical error in part (B).
In this sentence, the error is the use of the word "hardly" in part (b). The correct word to use is "hard". "Hardly" is an adverb that is used to mean "barely" or "scarcely", and it does not fit in the context of the sentence. The intended meaning in this sentence is that she has been working diligently or with great effort, which is conveyed by the adjective "hard".
Therefore, the correct word to use in part (b) is "hard", not "hardly".
Hence, the correct sentence formed will be "She has been working very hard to complete her project before the deadline."