疾病轮状模型的"轮轴"是（）。
A.生物环境
B.机体
C.社会环境
D.特异病原体
E.遗传因子
参考答案：B
唐诗《早发白帝城》《蜀道难》是脍炙人口的名篇，其作者是[ ]
A．李白
B．杜甫
C．白居易
D．王安石
_____ has been introduced to the students to help them make progress.
A．Many books as well as advice
B．Some advice as well as many books
C．Not only some advice but also many books
D．Some advice and many books
