题目

What has puzzled the scientists is that a slight change in its environment ______ have pushed the rare species over the edge into extinction.        A. would                      B. must                        C. shall                         D. should 答案：D下列各成语所反映的情景，不能用光的直线传播知识解释的是（　　）A．一叶障目B．镜花水月C．凿壁偷光D．形影相随