【题目】Even though we have made much progress in preventing pollution, yet much ________.
A.is remained to do
B.remains being done
C.remains to be done
D.is remained to be done

【答案】C
【解析】句意：虽然在防治污染方面我们已经取得了很大进步，但依然还有许多要做。remain to do这里需要用它的被动式remain to be done，所以答案是C。