What is ironic about the relationship between Darnay and Carton

A.

Darnay marries Lucie, but it is Carton whom Lucie feels great affection for.

B.

Darnay initially dislikes Carton, but it is Carton who saves Darnay from the guillotine.

C.

Darnay tricks Carton into switching places, but Carton agrees out of love for Lucie.

D.

Darnay comes to like Carton, but Carton betrays Darnay to the revolutionaries.