确诊二尖瓣狭窄的最可靠的辅助检查是
A．心电图B．X线摄片C．超声心动图D．心音图E．CT
参考答案：C
核糖（C5H10O5）是人类生命活动中不可缺少的一种有机物，它的相对分子质量为______，核糖中，碳、氢、氧三种元素的质量比为______；其中______元素的质量分数最大．
---- I stayed awake _______ 12 o’clock to wait for my husband to come back last night.
------ Then you _____have had a good sleep, did you?
A．until; mustn’t
B．till; can’t
C．before; should
D．when; would
