Personally I don't like C because the second "sentence" is merely a dependent clause, and has no main clause on which to depend - therefore it's not a sentence. D is OK, but I'm not over-keen on the parentheses. E would be my choice if there were a comma inserted after "eight"; as it stands (and this could also apply to D), it could read as though your host has invited you at, say, seven, but is in fact expecting you at eight because he/she knows you will be late. A and B, as QM says, are definitely wrong.