What's the matter _______ you? ( )
A:in
B:with
C:at
如图所示,一带负电的滑块从粗糙斜面的顶端滑至底端时的速率为v,若加一个垂直纸面向外的匀强磁场,并保证滑块能滑至底端,则它滑至底端时的速率 ( )
已知向量a→=(2,4),b→=(﹣1,1),则2a→﹣b→=( )
While in the university,we were offered a number of afterschool activities to________our social skills.