该图中,各点关系正确的是 ( )
A:A点比B点气压低
B:C点比B点气压低
C:D点比A点气压高
D:C点比D点气压低
B: Trigger must ____ ____ ____ ____with the crime, because he was at home when the crime took place.
在四棱锥P﹣ABCD中,PA⊥平面ABCD,△ABC是正三角形,AC与BD的交点M恰好是AC中点,又PA=AB=4,∠CDA=120°,点N在线段PB上,且PN=2.
(Ⅰ)求证:BD⊥PC;
(Ⅱ)求证:MN∥平面PDC.