下列具有细胞结构的是（　　）

黄铜是铜和锌的合金。某化学兴趣小组的同学在测定黄铜中铜的含量时，取黄铜样品40 g放入烧杯中，向其中加入200 g稀硫酸，恰好完全反应，反应后烧杯中剩余物的总质量为239.6 g。请计算：

诗歌赏析
                                                                                                 次北固山下
                                                                                                     王湾
                                                                                      客路青山外，行舟绿水前。
                                                                                      潮平两岸阔，风正一帆悬。
                                                                                      海日生残夜，江春入旧年。
                                                                                      乡书何处达? 归雁洛阳边。