They ____ a race with Class Four yesterday. ( )
A:had
B:have
C:has
如图,在棱长为2的正方体ABCD—A1B1C1D1中,O是底面ABCD的中心,E、F分别是CC1、AD的中点.那么异面直线OE和FD1所成角的余弦值为( )
It was not until dark ___ he was aware of ___ he thought was the correct way to solve the problem.