根据汉语提示填入适当的单词。

1. I think the calculator was _____ (发明) before the computer.

2. A stamp is used for _____ (寄) a letter.

3. Shoes with adjustable heels are used for _____ (改变) the style of the shoes?

4. What do you think is the most _____ (有用的) invention

5. I'm sorry I took your book by _____ (错误).