根据语境补全句中的单词。
（1）Do you know ________________（为什么）?
（2）It’s an ___________________（请柬）to my birthday party.
（3）You were in China for two __________________（年）.
（4）Now there is a big __________________（操场）.
（5）I don’t have anything to do. I’m _________________（无聊的）.