Comparing Angles After Folding a Rectangle

As shown in the figure, rectangle $ABCD$ is folded along its diagonal $BD$, carrying triangle $ABD$ to triangle $A'BD$, where $A'$ does not lie in the plane of the rectangle. (In the figure, $A$ denotes the original position of the folded vertex.) Let $\alpha$ denote the angle between the skew lines $CD$ and $A'B$. Determine, with proof, which of the following claims must be true:

1. $\alpha<\angle A'CD$ 2. $\alpha>\angle A'CD$ 3. $\alpha<\angle A'CA$ 4. $\alpha>\angle A'CA$