Sometimes children have trouble ________ fact from fiction and may believe that such things actually exist．
A.to separateB.for separatingC.separatingD.of separating在线课程C
句意：有时候孩子们很难把现实与虚构区别开来，可能认为那样的事真的存在。此题用have trouble/difficulty in doing句式，介词in可省略。