Which statement best describes the state$-$federal relationship regarding the insurance exchanges required by the Affordable Care Act?

a$.$

States may delegate management of insurance exchanges to private insurers pursuant to federal regulations.

b$.$

If states fail to design and operate insurance exchanges, the federal government will step in and do so$.$

c$.$

Each state is required to design and operate an insurance exchange.

d$.$

The insurance exchanges are solely in the purview of the federal government.