根据句意或中英文提示写出所缺单词。
1. Water covers about three quarters of the earth's ____ .(表面)
2. ____ (though) he is very clever, he doesn’t work hard at his lessons.
3. Are you ____ (sure) Mr Wang will come to our meeting?
4. ____ with life on Earth, life on Mars will be better in many ways.(比较)
5. The Great Wall is one of the ____ (unusual things that fill people with surprise) in the world.
