--- Liu Tao has never read the book The Adventure of Tom Sawyer , _________ he?--- _________. He told me it's very interesting. He'd like to read it again.
---- Do you know Jack well? ---- Certainly, we _________ friends since ten years ago.
The box is too heavy for me _________.
It _________ rain this afternoon, but I am not sure.
_________ the help of man-made satellites, we can know what the weather will be like in the next few days.
---- Is the physics problem _________? ---- Yes, I can work it out _________.