The issue is that the nephew did not know about the deed until after he returned from his deployment. For a deed to be delivered, there must be evidence that the grantee accepted it; an agent may receive a deed, but there must be evidence that the grantee knew about it and accepted it. I think, therefore, that A and B, though they make sense intuitively, are straight out because a person can't just unilaterally deed a property to another.
I don't think that D can be correct either, since it was in the form of a deed rather than a will. I've never heard of a gift causa mortis before, but it sounds like a gift made in the expectation of imminent death. Since the homeowner was ill and his actions suggested his intent for his nephew to have the house on his death, I'm going to go with C as the correct answer.
