1,They live at 83 Son Tay Street
→Their adress is at 83 Son Tay Street
2,How wide is this room?
→What is the width of this room?
3,Don't forget to lock the front door before you leave
→Be sure to lock the front door before you leave
4,I am very glad to see you all again
→It's such a pleasure to see you all again
5,It is necessary to learn english well
→Learning English well is necessary.