等差数列{an}的前n项和为Sn，a2+a8+a11=30，那么S13值的是[ ]
A．130
B．65
C．70
D．以上都不对
答案：A
She has been teaching in a school since she graduated, so she is not __________ to associating with business people. [ ]
A. addicted
B. devoted
C. accustomed
D. admitted
在硅（或锗）本征半导体中掺入微量的（）元素，就形成了主要由自由电子导电的电子型半导体，即n型半导体。
A.三价
B.四价
C.五价
