区分纯净水和和矿泉水的最佳方法是[ ]
A．观察是否澄清、透明进行区分．
B．品尝味道
C．加肥皂水，搅拌，观察有无泡沫进行区分
D．蒸干
答案：C
---European scientists announced that the speed of light isn’t the speed limit.
---Perhaps it is the biggest challenge to Einstein’s Theory of Relativity. No one _____ any crack in his
theory for more than a century. [ ]
A. has found
B. found
C. had found
D. would find
房室瓣关闭，见于
A．等容收缩期初B．等容收缩期末C．等容舒张期初D．等容舒张期末
