计算：（﹣a）5×（a2）3÷（﹣a）4的结果，正确的是 [ ]
A．a7
B．﹣a6
C．﹣a7
D．a6
答案：C
5．下列物质属于苯的同系物的是( )
— When are you going to Hainan?
— I am going there _____ June 8, 2007. [ ]
A. with
B. on
C. at
D. in
