10．听第12段材料，回答第13至15小题．听之前你有5秒钟时间阅读相关小题，听完后你有5 秒钟时间作答．
13．Why do they collect the rubbish along the river？
A．To stop the river from being polluted．
B．To sell it for money．
C．To see the river every day．
14．How many volunteers do they have？
A.10．
B.14．
C.24．
15．When do they do the volunteer work？
A．At 8：30 every morning．
B．After lunch at noon．
C．After dinner every evening．
