I am an English language learner and was trying a to solve an error spotting set but I am not getting any error in the question below. There is a mistake in the statement classified into 3 parts (A, B & C).
Kindly help me detecting the error with explanation of rule behind that.
Essay writing is an art (A) / that requires many planning (B) / on the part of the writer. (C) / No Error (D)
The answer set says there is an error in part B, but with no explanations.