选用方框中所给单词的适当形式填空。

—How long did Qing Dynasty rule（统治）over China?
—Over two _______ and a half.
Don’t worry about her. She is old enough to think for _______.
Their classroom is _______, and they have to wait for their teacher to open it .
________ on the ice is a popular outdoor activity in the north of China.
The students are so ________ because they will go to the park for a picnic tomorrow .