The correct option is C is
Our subject in the given sentence is James Greaves. Author and painter are not separate subjects, but simply a phrase that tells us more about the subject. Therefore, we need a singular verb to agree with our singular subject. In the given sentence, we have 'are' which is a plural verb, we need to change that to a singular verb (this rules out option D). From the given options, only option C has a singular verb: is, which makes it the correct option. Verbs mentioned in options A and B are plural in nature and hence would not work in the given context.