关于瓦斯的描述正确的有（）
A、主要成分是甲烷
B、无色无味
C、无毒，但不利于呼吸
D、比空气轻
参考答案：A, B, C, D
腹大胀满，或见青筋暴露，面色晦滞，唇紫，口干而燥，心烦失眠、时或鼻衄，牙龈出血，小便短少，舌质红绛少津，苔少或光剥，脉弦细数，宜选方
A．肝脾血瘀水停B．心肾不交C．肝郁气滞D．肺气不宣E．阳气不振，水湿内停
The student asked her professor if he would have gone on the space ship he did know earlier.
A．if he knew
B．if he knows
C．he had known
D．had he known
