题目

玉米花药培养的单倍体幼苗，经秋水仙素处理后形成二倍体植株。下图是该过程中某时段细胞核DNA含量变化示意图。下列叙述错误的是( ) A．a～b过程中细胞一定不会发生基因变化 B．b-n和f-g过程的发生是一样的 C．c点后受秋水仙素作用，细胞内各染色体组的基因组成可能相同，也可能不同 D．f～g过程后，DNA与染色体的比例是1:1近年来，中小学生的健康问题日益引起人们的关注。请你以How to keep healthy 为题，写一篇80词左右的短文，谈谈你的看法和建议。要求：主要包括以下内容，可以适当发挥。文章开头已给出，不计入总词数。1.列举中小学生面临的健康问题，如go to school without breakfast, play computer games, watch TV, drink or smoke,,,2.提出保持健康的合理建议；3.发表自己的看法。How to Keep HealthyEveryone needs to keep healthy today, especially we students. But we don’t know the importance of keeping healthy._____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________