The correct option is E flatter Lord Mayor's vanity.
The correct answer would be option D, where the Earl is trying to flatter the Mayor in order to get his cousin married to the latter's daughter. He already acknowledges the latter's generosity and his indebtedness to him. But the objective is to flatter him. Their difference is already establishes, so there is no effort to further emphasize them. Hence, options A,B,C and E are incorrect.