6. I believe the answer is: C. used congressional caucuses
Congressional caucuses refer to a group of congress who held the same objective to pass a type of legislation that would benefit them in some ways. They do not necessarily belonged in a same party, and they often trade favours in order to provide each others with votes during the creation of legislation.
8. I believe the answer is: Political parties
In united states, the National Conventions is being held in order to appoint the cnadidates that are going to be running for the presidential position. In the convention, each parties would nominate their own appointee which usually have similar belief with the parties.