动物对于一个生态系统来说是很重要的，这是因为 （  ）

小明同学用已经调节好的天平测量物体的质量，操作情况如图所示，它的错误有

阅读下面的诗文，回答相关问题。

                                                                                                          《饮酒》
                                                                                                            陶渊明

                                                                                             结庐在人境，而无车马喧。
                                                                                             问君何能尔，心远地自偏。
                                                                                             采菊东篱下，悠然见南山。
                                                                                             山气日夕佳，飞鸟相与还。
                                                                                              此中有真意，欲辩已忘言。