The answer is flourish. Incentive has nothing to do with this sentence. You could say that he "...signed his name with a bold and dramatic sweep", and that would basically be the same thing.
The answer is C. Bethany has to be capitalized because it’s a name (proper noun) and Honda Civic also has to be capitalized because it is also a proper noun. Green doesn’t have to be capitalized because it is an adjective.
