Maybe you could start by writing the components of A, for example . The same for B: .

Do the same for C and D.

Now, C is parallel to A. It means that their cross product is null. (see Cross Product -- from Wolfram MathWorld). So do the cross product between those 2 vectors and equal it to 0.

D is orthogonal to A, it means that their dot product is null.

Can you take it from there?