题目

12．下列关于种群、群落和生态系统的叙述中，正确的是( ) ①气候、食物、天敌和传染病都将影响到大熊猫的种群密度 ②在弃耕农田演替至森林过程中，物种丰富度和有机物总量均不断增加 ③农田生态系统对太阳能的利用率高于森林生态系统 ④与北极苔原相比，热带雨林抵抗力稳定性强、恢复力稳定性弱 A．①②                                      B．①②③ C．①③④                                 D．①②③④根据首字母拼写单词，完成短文。 Mr Smith has two sons and one d________. The children all l________ with him in the Moon T________. It is not so big, but it is quite beautiful. There are many interesting places in it. You can visit them here and there. There is a big s________ pool in Moon Town. The children like to swim there. They can have a g________ time in the swimming pool.