1. you (модальный глагол) use the office phone for private talk. 2. you (модальный глагол) come if you don`t want to. 3. i know you are a careful driver but you (модальный глагол) drive so fast. 4. schoolchildren (модальный глагол) wear jewelllery when at school.

You can use the office phone for private talk
you cant come if you dont want to
I know you are a careful driver but you mustnt drive so fast.
school children should wear jewellery when at school

1 Must
2 can
3 needn't
4 must