The Affordable Care Act (ACA), Popularly Referred to as Obamacare

The Affordable Care Act (ACA) , popularly referred to as Obamacare, increased the percentage of Americans covered by health insurance.A Supreme Court ruling, however, made optional the funding of coverage for many lower-income people.Why was this the case?

A) The Court ruled, on federalism and states' rights grounds, that the national government could not compel states to expand Medicaid coverage, under the ACA.
B) The Court ruled that states could not be required to offer subsidized health-care policies under their insurance exchanges, as required under the ACA.
C) The Court ruled that increased use of categorical grants to states to fund the health care of lower-income populations posed a conflict with the Tenth Amendment.
D) The Court ruled that the expansion of Medicaid in every state, as required under the ACA, represented an unfunded mandate.