We have only one Earth. It’s our common _.

--What’s that?  --It’s an________．

--- What’s your favourite subject, Mike? --- _________. It’s interesting.

----Where is Tom?----He’s left a(n) _____ saying that he has something important to do.

--Why do you get up so early in the morning?---I make it a ______ to get up before 7am to read English.