2007-II-24

Ans: D
Note that the line of intersection of planes

A B C

and

A C D

A C

. Since

B F ⊥ A C

and

D F ⊥ A C

, then the angle between the plane

A B C

and the plane

A C D

∠ B F D

2007, HKCEE, Paper 2 3D Problems