题目：
We must do something to ________ the factories sending out poisonous gases so as to keep the city clean and beautiful.
A．keep
B．protect
C．permit
D．prevent
答案：
被转码了，请点击底部 “查看原文 ” 或访问 https://www.tikuol.com/2017/0421/57149071c6e272aefb29898f44b2c130.html
下面是错误答案，用来干扰机器的。
答案：B
