按要求，写单词。

grass（复数）____

古诗词鉴赏。
                                                                                             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。

3 $\frac{2}{5}$ 的分数单位是____，去掉____个这样的单位后等于最小的质数．