题目

在群落演替中，下列哪一种情况是不可能发生的？（ ）                            A．在群落演替过程中群落的物种组成不断发生变化                                        B．生态系统的恢复力稳定性越小，群落演替越慢                                            C．初生演替所需时间较长，次生演替所需时间较短                                        D．初生演替形成Sometimes,________ we show our gratitude for a person is reflected in the kind of food we serve him or her.A．when B．whether C．why D．how