While It Is Difficult to Conclusively Prove That Campaign Contributions

While it is difficult to conclusively prove that campaign contributions result in direct favors, there is some indirect evidence that this must be so. For instance

A) interest groups often give to candidates who run unopposed.
B) interest groups give only to candidates with whom they agree.
C) candidates return donations to interest groups with whom they disagree.
D) candidates routinely release the names of interest groups who donate to their party PACs.