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. Much of the students in the class

B. are weak in Mathematics and therefore

C. the Headmaster has arranged for special tuition

D. in the evening after class-hours

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