Final answer:
The correct antonym for an insincere expression of concern is 'genuine,' meaning something true and sincere.
Step-by-step explanation:
The question asks for the antonym of an insincere expression of concern. The word 'insincere' indicates a feigned or pretended feeling, meaning it is not expressed genuinely. Of the options given, 'genuine' serves as the correct antonym, as it refers to something sincere and authentic, without pretense. Therefore, the answer to the given question is b) genuine.