某中学到离学校15千米的某地旅游，先遣队和大队同时出发，行进速度是大队的1.2倍，以便提前半小时到达目的地做准备工作．求先遣队和大队的速度各是多少？

The director had her assistant _____ some hot dogs for the meeting.  [ ]

A. picked up                          

B. picks up    

C. pick up                                

D. picking up