3,4
5 не нужно
Спасибо:)

№3
it is very quiet
the lessons have begun
the students are working
they have been working since 9 o'clock
the bell will go in half an hour

№3
1. Where do you study?
2. How many years have you been studying here?
3. Have you (ever) studied anywhere else?
4. When did you leave school?