—Sorry. I ______ a text message just now.
A:had answering
B:have answered
C:would answer
D:was answering
如图所示,水平力F将物体P压在竖直墙上,物体P始终处于静止状态,则下列正确的是( )
设函数f(x)=sin(wx+2π3)+sin(wx-2π3)(w>0)的最小正周期为π,则( )
(I)求证:BE∥平面ACF;
(II)求平面BCF与平面BEF所成锐二面角的余弦角.