题目

—Is this a teacher's office? ( ) —Yes, _________.A.he is B.it is C.she is 答案：【答案】B【解析】句意：这是老师的办公室吗？问句用this，答句用it，故选B。13．已知等差数列{an}满足：a1+a4+a7=2π，则tan（a2+a6）的值为（　　）A．-$\sqrt{3}$B．-$\frac{\sqrt{3}}{3}$C．$\frac{\sqrt{3}}{3}$D．$\sqrt{3}$