When you are more than ______ you can be a worker in factories.
A:18 years old
B:18 old year
C:18 year olds
(Ⅰ)证明:平面PAD⊥平面ABFE;
(Ⅱ)求正四棱锥P﹣ABCD的高h,使得二面角C﹣AF﹣P的余弦值是 223 .