the usesage of "the number of"

English as a Second Language English Vocabulary, Grammar and Idioms
1

hello,
My name is Trang
I am preparing for TOEIC exam.^^ and I don’t understand why answer is " require", but not " requires" and the different useage between “the number of” and “a number of”
please explan to me.^^

and this is the question: the number of users who… support has increased since the company released the lastest version of its software
A. require B. requires

Thank you very much for your helping^^
Trang.

2

‘The number of users’ is singular - one number. That is why ‘require’ is correct.

The number of - in this case the sentence is speaking about a specific set of users - the ones who require support.
A number of - is non specific.

3

thank you, teacher.^^