尿后余沥不尽的病因是（）
A.肾精亏虚
B.肾阴亏虚
C.肾气不固
D.膀胱湿热
E.肾虚水泛
参考答案：C
E-mail, as well as telephones, _______an important part in our daily communication.
A．play
B．have played
C．are playing
D．is playing
氮气中混有少量氢气、二氧化碳和水蒸气，欲获得干燥纯净的氮气，可采用下列操作： ①通过浓硫酸 ②通过填充氧化铜的加热管 ③通过氢氧化钠溶液 ④通过浓盐酸最好的组合顺序是[ ]
A.①→②→③
B.③→②→④
C.③→②→①
D.④→②→③
