简述广告公司的类型与服务范围。
参考答案：
①广告代理公司
②广告制作公司
③媒介（购买）公司
It suddenly occurred to him _____ he had left his keys in the office.
A．whether
B．where
C．which
D．that
胭动脉的主要分支有
A．膝上动脉
B．膝中动脉
C．膝下动脉
D．胫后动脉
E．胫前动脉
