暮江吟
                                                                                                                                        唐·白居易
                                                                                                                一道残阳铺水中，半江瑟瑟半江红。
                                                                                                                 可怜九月初三夜，露似珍珠月似弓。

夜盲症和脚气病是因为体内分别缺乏（　　）

神经系统结构和功能的基本单位是____。