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.

①我性格开朗活泼，爱好广泛               ②妈妈说我做事认真，从不马虎

③我的最大缺点就是爱哭鼻子                ④老师说我能力强，是得力助手

如图所示为探究磁场对电流的作用的实验装置，闭合开关，观察到直导线AB运动起来，说明磁对电流有力的作用，将磁体两极对调，观察直导线AB的运动方向，这是为了探究力的方向与 ____关系，实验中选用铝导线而不用铜导线是因为铝的 ____较小；将电路中的电源换成灵敏电流计并将滑动变阻器的接入电阻调到最小，可用来探究 ____产生的条件．