context: Much of the work of the Scottish Parliament is done in committee. The role of committees is stronger in the Scottish Parliament than in other parliamentary systems, partly as a means of strengthening the role of backbenchers in their scrutiny of the government and partly to compensate for the fact that there is no revising chamber. The principal role of committees in the Scottish Parliament is to take evidence from witnesses, conduct inquiries and scrutinise legislation. Committee meetings take place on Tuesday, Wednesday and Thursday morning when Parliament is sitting. Committees can also meet at other locations throughout Scotland.
question: Which group has a primary role scrutinizing witnesses?