No, gay marriage isn't "A". But this isn't like a test where you have to meet all 4 definitions. By definition, and I'm just using the source that you brought up, if any one of those 4 are met it is a "marriage". I can be (B) and not (A) or be (C) and not necessarily fit into (B)... so why does a (D) have to meet (A) too?
The point is that the world isn't black and white. And you can't fit everyone and everything into neat little columns. It just doesn't work.
