营运资本系指企业的流动资产，它包括（）
A.现金
B.短期证券
C.应收帐款
D.存货
参考答案：A, B, C, D
He often come to work early and he is ____ late for work.
A．usually
B．never
C．often
D．always
通常用ELISA测定的OCV应（）
A.＜5%
B.＜10%
C.＞10%
D.＜15%
E.＞15%
