【阅读短文，从方框中选择适当的单词填空（每词限用一次）．winteractivealwaysnowhyBillisagoodboy．He'ssmart．Heloveshisschoolandisalways（86）___inclass．Everytimetheteacherasksa】

　　阅读短文，从方框中选择适当的单词填空（每词限用一次）．

　　winter active always no why

　　Bill is a good boy．He's smart．He loves his school and is always（86）___ in class．Every time the teacher asks a question，Bill puts up his hand．Sometimes his answer is wrong，but the teacher

　　（87）___ smiles and says，"Good，Bill．But is there a better answer to my question？"

　　This morning the teacher asked，"Swallows（燕子）go to the south before （88）___ comes．But（89）___ don't cats and dogs go to the south for the winter？As usual，Bill put up his hand and said loudly，"Because they have （90）___wings（翅膀）．"