The correct option is D flatter Lord Mayor's vanity.
Option D is the correct answer. The Earl of Lincoln is stating the generosity of the Lord Mayor and expressing his gratitude for all he had done for the former amongst others. He praises the Mayor, and also states that there is no one who could compete with him. There is no indications of the Earl's reciprocity in being generous, or bringing out the differences among them. Getting him to agree to the marriage is the ulterior motive. The Earl's acknowledgement of the Mayor's deeds is present, but his flattering is more apparent and obvious. Therefore, options A,B,C and E are incorrect.