please explain 1000 sc question

[rattanas]

Part of the proposed increase in state education spending is due to higher enrollment, since the number of students in public schools have grown steadily since the mid-1980’s and, at nearly 47 million, are at a record high.
(A) enrollment, since the number of students in public schools have grown steadily since the mid-1980’s and, at nearly 47 million, are at
(B) enrollment, with a number of students in public schools growing steadily since the mid-1980’s and, at nearly 47 million, reaching
(C) enrollment: since students in public schools have grown steadily in number since the mid-1980’s and, at nearly 47 million, have reached
(D) enrollment: the number of student in public schools has grown steadily since the mid-1980’s and, at nearly 47 million, has reached
(E) enrollment: students in public schools have grown steadily in number, since the mid-1980’s and, at nearly 47 million, are at

[astrologer]

A: Not gramatically correct. Would be correct if first part of the sentence would be in past participle instead of present tense.
B: 'a number' is incorrect
C: suggest that students have reached high and not their number .. wrong that is why.
D: Correct. Uses 'the number of students' with right grammar and no unweildy words
E: Same error as C

[chidcguy]

Please Please underline the part of the Question that needs to be modified

Here are my reasons

the number of is always singular.

A is wrong for that reason

A, B & E are also wrong for another reason that they do not continue the sentence in present perfect tense. has reached a record high vs are at a record high.

students in public schools have grown steadily in number

confusing and passive as the sentence intends to say that the number of students in PS has grown steadily. number of students has grown steadily is better than than the students growing in number. also, the have reached sounds like students (not their number) have reached 47 million

C is out

D is correct because it uses the number of students and singular has, also continues the present perfect