1. They must do duty, as we must do .

　　2. We have kept promise; let them keep .

　　3. All of us are the students of , of that woman standing over there.

　　4. In spite of gray hair, the old man appears ten years younger than he is.

　　5. The group is waiting for plane to Beijing.

　　6. Either the student or the teacher must have eaten lunch here.