群落演替。
参考答案：
生态系统内的生物群落随着时间的推移，一些物种消失，另一些物种侵入，出现了生物群落及其环境向着一定方向有顺序的发展变化过程。
蝗虫进行呼吸作用的器官是 [ ]
A．气管
B．气门
C．鳃
D．肺
There were so many cars held up by the heavy rain on the road that we had no but to wait. [ ]
A. alternative
B. difference
C. relation
D. opposition
