Read the passage and choose the best answer

I think it is necessary for students to wear uniforms when they are at school.
Firstly, uniforms encourage students to be proud (14)………………..being students of the school they are going to because they are wearing the uniforms with (15)………………..bearing their school’s name.
Secondly, wearing uniforms helps students (16)………………..equal in many ways. Everyone starts (17)………………..the same place, whether they are rich (18)………………..poor. They are really friends (19)………………..one another under one school roof.
Finally, wearing uniforms (20)………………..practical. You don’t have to think of what to wear every day.
Therefore, all students, from primary to high (21)………………..should wear uniforms.

Câu 14 : (14)....................

A. of

B. in

C. at

D. on