《礼记》中“鹦鹉能言，不离飞鸟，猩猩能言，不离禽兽。今人而无礼，虽能言，不亦禽兽之心乎？”对这句话理解正确的是（    ）

下图表示一个细胞进行细胞分裂过程中，细胞核内染色体数目及染色体上的DNA数目的变化，则下列叙述正确的是：

    To save time, many Americans buy foods which can be quickly made ready for the table. On holidays, families enjoy delicious meals. For example, on Thanksgiving Day, the fourth Thursday in November, family members get together for a turkey dinner with pumpkin pie(南瓜派).

    People can easily find fast food chains(连锁店),such as McDonalds' and KFC, in most of the big cities in the world.

    These years, many people have taken more and more care of their health while eating. They come to know eating too much meat will make them overweight. Many of them are also worried about food addictives(添加剂). Some of them may be harmful to the body.

已知的维生素有20多种，它们多数在人体内不能合成，需要从食物中摄 取，人体缺乏下列哪种维生素，会引起夜盲症（    ）