饮用矿泉水可分为碳酸水、硅酸水和锶水等几大类.此外还有锌、锂、溴、碘及硒等的矿泉水,这里“锌、锂、溴、碘、硒”指的是( )
A.元素
B.原子
C.分子
D.单质
答案:A
婴幼儿上呼吸道的解剖特点不正确的为()
A.管腔狭窄
B.黏膜柔嫩
C.血管丰富
D.鼻窦发育较差
E.咽鼓管呈斜位
There _____ great changes in our country in the past twenty years. [ ]
A. have been
B. has been
C. have had
D. has had