B. Choose the best words or expressions and complete the passage. （5分）

Bill is smart. He is a good boy. He loves his school and he is1 active(活跃的）in class. Every time the teacher2 a question, Bill puts up his hand. Sometimes his answer is3 , but the teacher always 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 before4 comes. But why do not cats and dogs go to the south for the winter?"As usual, Bill puts up his hands. "Yes , Bill?"said the teacher.

Bill stood up and said loudly, "because they have5 wings(翅膀). "