登高作业时，必须有（）以上在场。
A.二人
B.三人
C.四人
D.五人
参考答案：A
He waited until it was dark ____ nobody could see him clearly.
A．so that
B．in order to
C．although
D．however
少阳经的引经药为：
A．疏肝利胆B．健脾和胃C．逐瘀退黄D．温阳化湿E．清热利湿
