∫e, f and g are the midpoint of PC, PD and CB respectively, ∴EF∥CD, cg∨. DH，

∴ Quadrilateral CDHG is a parallelogram, cdhg.

∴ef∨GH。 ∴ four points EFHG four points * * * surface.

FH∨PA is here again.

Dad? Aircraft EFGH, FH? EFGH plane

∴PA∥ airplane ..

(2) Solution: ∵ The projection of point P on the plane ABCD is point D, ∴PD⊥ plane ABCD.

That is, PD is the height of the triangular pyramid P-ABC.

And S△A? BC = 12×ab×BC = 12×2×2 = 2。

∴ volume of triangular pyramid p-ABC v =13s △ ABC× PD =13× 2× 2 = 43.