边缘效应
参考答案：指两个截然不同的生态系统的边缘地带，通过对两个系统的连接，扩大能量转化和物质循环规模，从而使两个生态系统效应均有所提高的现象。
Could you tell me___________?
A．who can help us organize the show
B．how long you have bought the car
C．what was your favorite subject
D．how many students are there in your class
在管材中塑料管是（）管。
A、金属
B、无机非金属
C、非金属
D、复合
