信息利用服务的意义在于______。
A．实现信息价值
B．发挥信息作用
C．利用信息增值
D．便于信息查找
参考答案：A,B,C
晶闸管有阳极、阴极和控制极，其内有四层PNPN半导体，（）个PN结。
A.2个
B.3个
C.4个
D.5个
"You can't have this football back _____ you promise not to kick it at my cat again. " the old man said
angrily. [ ]
A. because
B. since
C. when
D. until
