Tom hasn't appeared for 10 days. So I promise his parents: “I'll report back, the moment I ________ him.”

②∠AOC＋∠BOD＝90°；③若OC平分∠AOB，则OB平分∠COD；④∠AOD的平分线与∠COB的平分线是同一条射线. 其中正确的个数有（   ）

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.

设三位数$n=100a+10b+c$,若以$a,b,c\in \left\{1,2,3,4\right\}$为三条边的长可以构成一个等腰(含等边)三角形,则这样的三位数n有（　　）