Which statement reflects a unique obstacle to national health insurance in the U.S.? a. The conservative party in the U.S. is more open to measures that socialize risk than the conservative parties in much of Europe have been. b. The private health insurance industry became much larger in the U.S. than in other countries and has much more political power. c. The power of public-health professionals to emphasize investment in prevention over curative care. d. The lack of health services researchers to determine the most effective treatments and their costs