they can help control

Trees and forests are like the lungs of the earth,they can help control______.
A.polluting B.pollute C.pollution

我知道空格处需要填一个名词，可是为什么polluting这样的动名词不行。而答案是pollution

they want to know ()to help us. b.what they can;c.how they can they can help peopleto w_____out many problems they can't do easily. _______ that they refuse us, who else can we turn to for help? our teachers always do what they can to help us with our studies They can can what they can can,but can't can what they can't can是什么意思 who can help me ? Who can help me? WHO CAN HELP ME！！ can you help me Who can help me ~!~!!