集团客户网络服务等级协议规定铜牌级客户的跨国数据专线业务保障等级为()
A.普通级
B.AAA级
C.AA级
D.A级
参考答案:C
—When _________ you _________ old friends?
—The day before yesterday. [ ]
A. will; visit
B. did; visit
C. have; visited
D. did; visited
简述人体基本运动原理。