产生激光的条件有（）
A.光学谐振腔
B.激励能源
C.具有亚稳态的工作物质
D.自发辐射
E.韧致辐射
参考答案：A, B, C
The children went home from the grammar school, their lessons ______ for the day.
A．finishing
B．finished
C．had finished
D．had been finished
下面各项中，属于企业所有者权益的是( )。
A．银行借款 B．债券 C．商业信用 D．资本公积金
