在生态系统中,一些有害物质可以通过食物链在生物体内不断积累,使其浓度随着消费者级别的升高而逐步增加,这种现象叫做( ) A.遗传
已知马蛔虫体细胞内有2对染色体,下列图示能正确表达马蛔虫生殖细胞中染色体组成的是 A. ①② B. ②③ C. ①
苔藓植物比蕨类植物长得矮小的原因是 ( ) A、苔藓植物只能生活在阴暗潮湿的地方 B、苔
I like playing violin, but Tom likes playing basketball. A. the … / B. the … the C. / … the D. / … /
2010年青海玉树地震发生后,地震预报再次成为人民群众关注的焦点。某地震专家指出,从现在的地震学研究水平来看,精确的短期预报是不可能实现的
This exam is very important for her. She won’t go home ______ the exam. A. until after B. after until C. until D. from
—I can't get the book on the shelf. —Why not have someone tall enough ________ it then? A. to take B. take C. taking D. takes