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In the following questions, a sentence has been divided into four parts and marked a, b, c and d. One of these parts contains a mistake in grammar Idiom or syntax. Identify that part and mark it as the answer.

A. Did he say he will

B. bring the book tomorrow?

C. He has been promising so

D. for the past seven days

Please do not use chat terms. Example: avoid using "grt" instead of "great".