20．聽短文，根據(jù)短文內(nèi)容在各題所給的 A、B、C 三個選項中，選出一個最佳選項．（本題聽兩遍）
21．Mr．Smith is explaining the importance of in the science lesson
A．a(chǎn)ir B．food C．water
22．Why didn't the students want to answer the teacher？
A．Because they think the question is too easy．
B．Because they don't know how to answer the question．
C．Because they want to answer the question after the lesson．
23．What does the water in the river behind the boy's house look like？
A．Black B．Red C．Green
24．Why can't people swim in that river now？
A．Because there are dangerous animals in the river．
B．Because the river is too dirty．
C．Because the water is too deep．
25．What did Mr．Smith want to do？
A．He wants to swim in the river．
B．He wants to go fishing in the river．
C．He wants to make water clean．
