—Next Wednesday.
A:when they will leave
B:when will they leave
C:when they leave
D:when do they leave
甲、乙两地同在30°E上,甲地纬度是50°N,乙地纬度是20°S,则甲地在乙地 ( )
若e1→·e2→是夹角为60° 的两个单位向量,则a→=2e1→+e2→,b→=-3e1→+2e2→的夹角为( )