问题
选择题
All possible means ___ been tried to stop the air______.
A．has, polluted
B．have, polluting
C．have, being polluted
D．has, being polluted
答案
答案：C
第一空考查主谓一致means是单复同形的名词本句中有all视为复数；第二空考查短语stop …(from)…“阻止做某事”空气应是被污染要用动名词的被动式。句意为：已经尝试了所有的方法来阻止空气被污染。选C
