Final answer:
The 2010 Supreme Court decision in Citizens United v. FEC enabled corporations, unions, and non-profit organizations to spend freely on independent expenditures to support or oppose candidates.
Step-by-step explanation:
The correct answer is d. The 2010 Supreme Court decision in Citizens United v. FEC. This decision held that corporations, unions, and non-profit organizations have the right to spend freely on independent expenditures to support or oppose candidates, as long as they are not coordinated with candidate campaigns. The decision removed certain restrictions on campaign spending by these entities, leading to the emergence of super PACs and increased influence of money in politics.
Learn more about Campaign spending by corporations, unions, and non-profit organizations