The main difference between a joint committee and a conference committee is what?

Joint Committees are set up to expedite business between the houses and to help focus public attention on major matters, such as the economy, taxation, or scandals. They include members from both houses of Congress who conduct investigations or special studies.

Conference committees are special joint committees that reconcile differences in bills passed by the House and Senate. A conference committee is made up of those members from the House and Senate that originally considered the bill.

So the answer is: C. joint committees perform investigative or house keeping duties; conference committees iron out differences in bills from both houses.