A:why it was that
B:how was it that
C:was it that why
D:it was that how
一物体静止于固定斜面上,则下面说法中正确的是( )
空间四个点P、A、B、C在同一球面上,PA、PB、PC两两垂直,且PA=PB=PC=a,那么这个球面的面积是____