根据句意，用所给词的适当形式填空。

1．The famous                （sing） is going to give a concert to raise money for charity．

2．--Do you have a pen pal, Jeff?

    --Yes．He's an               （America） boy．

3．I don't understand what they are saying because they speak too             （quick）．

4．I didn't finish               （write） my test because I ran out of time．

5．All of us felt               （excite） and proud when we watched China's first-ever spacewalk at 4:43 pm on September 27, 2008．