企业在进行成本核算时，必须按费用的受益期限确定其归属期，这是成本核算的( )原则。

等腰三角形有一个外角是100°，那么它的的顶角的度数为（     ）。

It’s impossible for him ______.

A．talk with his parents about his mistakes

B．talking with his parents about his mistakes

C．talked with his parents about his mistakes

D．to talk with his parents about his mistakes

下列不属于性传播疾病的是（）。

A.梅毒

B.淋病

C.软下疳

D.尖锐湿疣

E.乙肝

下列选项中哪一项直接关系到整个网络教室的性能（）。

A.教师机配置的档次

B.学生机配置的档次

C.多媒体传输控制卡

D.多媒体传输电缆