用所给单词的适当形式填空。

1. Students are supposed              (arrive) at school on time.

2. —Thank you for your kind               (invite).

    —It's a pleasure.

3. What should you do when you meet for the             ( one) time?

4. I guess you should             (ask) what you were supposed to wear.

5. His bike is            (difference) from mine.

如图所示，一根均匀的木条AB长为L。将其放在水平桌面上，使B端伸出桌面L，在伸出桌面部分的上方放一个长L，重3N的均匀木块恰能使A端离开桌面，则木条重     N。