It's difficult to tell the difference between butterflies and moths.蝴蝶和飞蛾很难区别。Sometimes it's difficult to draw a line between backbiting and malicious gossip.背后中伤和歹毒的流言蜚语，有时很难区别。Brought up in town, the boy finds it difficult to separate a poplar from a willow.那男孩是在城里长大的，所以觉得很难区别杨树和柳树。