用方框中所给单词的适当形式填空，，每词仅用一次。

Teachers often tell their students about the _________ of learning how to learn.
Do you know that Bill Gates gave away________ of dollars in 2010?
You’d better go to bed early, or you will feel_____ in class.
Think it over before you make a ________.
We’re in the __________ grade now. And we should learn hard.