Read this excerpt from a concluding paragraph Jason has drafted from his research outline on the hazards of playing football and answer the question.

(10)Currently, the best way to prevent concussions is to wear anti-concussion helmets. (11)If the NFL cares about its players and their safety, it will mandate that every player wear an anti-concussion helmet during every practice and for every game. (12) By showing its support of these protective helmets, the NFL will be encouraging the manufacturers to further improve them.

Which sentences, if added after sentence 12, would provide the most effective conclusion to support the author’s argument?

a. (13)Will the availability of improved safety helmets guarantee that they will be used? (14) No, because many may think it fosters a less masculine image of physical strength. (15)By regulating their use, however, every player has a better option for his future.
b. (13)If the NFL approves the regulation, it will demonstrate its commitment to the future of its players. (14)It’s about time that we all pull together and offer athletes more than "atta-boys" for the risks they take to entertain us. (15)After all, haven’t we moved past the time of gladiators?
c. (13)Fans of the sport cannot continue to support a practice that leads to over 150 concussions every season. (14)Please consider a sound solution. (15)Support the mandatory use of anti-concussion helmets.
d. (13)Although NFL players receive generous salaries, injured players can no longer fulfill their contracts. (14)Often the effects of concussions prove to be more serious at later points in a player’s life. 15)It’s time for fans to assist players by supporting the regulated use of improved safety helmets.