Grammar

"I will reach the classroom later." A pronoun (a/an/the) is required for a non-specific noun like "classroom".

"The course was postponed because the number of students did not reach the requirement." You must make sure that all parts of the sentence match tense. In this case, you had a past tense verb "was postponed" with a present tense verb "does not reach", so I

Gaw Kai Muh Hi Experts,please mark my sentences.I will reach classroom/the classroom later.The course was postponed because the number of students does not reach the requirement.

Do you mean that not enough students enrolled in the course so they could not offer it?

PsychowordA pronoun (a/an/the)

Those are not pronouns; they’re articles.

PsychowordYou must make sure that all parts of the sentence match tense.

That is not a requirement if the shortage still exists.

Gaw Kai MuhI will reach classroom/the classroom later. The course was postponed because the n

Hi Geek,
Yes.

Then say "The course is postponed because not enough students enrolled in it." or "The course was postponed because minimum number of students required to hold the course was not met."

There are dozens of ways you can say this.

Thank you for the correction on pronouns versus articles. I can't believe I made that mistake.

As for the second sentence, in the way it was written, the tense needed to match. It cannot make sense for the deciding party to make a decision in the past to postpone a course based upon enrollment numbers in the present.

Using the present tense shows that there is still a lack of students. If this is the case, then backshifting is optional.