Alarge percentage of the money spent on political campaigns during the 1980s and 1990s came from

It came from unregulated soft money

Soft money is unregulated which means that there is no evidence or records of how the money was donated and by whom. Unlike this, hard money is that money which is regulated and it is known who donated it. Hard money is donated usually by people such as lobbyists or huge corporations and companies.

First D. Then C. Then B. Then A.