Each bill goes through several stages in each house including consideration by a committee and advice from the Government Accountability Office. Most legislation is considered by standing committees which have jurisdiction over a particular subject such as Agriculture or Appropriations. The House has twenty standing committees; the Senate has sixteen. Standing committees meet at least once each month. Almost all standing committee meetings for transacting business must be open to the public unless the committee votes, publicly, to close the meeting. A committee might call for public hearings on important bills. Each committee is led by a chair who belongs to the majority party and a ranking member of the minority party. Witnesses and experts can present their case for or against a bill. Then, a bill may go to what is called a "mark-up" session, where committee members debate the bill's merits and may offer amendments or revisions. Committees may also amend the bill, but the full households the power to accept or reject committee amendments. After debate, the committee votes whether it wishes to report the measure to the full house. If a bill is "tabled" then it is rejected. If amendments are extensive, sometimes a new bill with amendments built in will be submitted as a so-called "clean bill" with a new number. Both houses have procedures under which committees can be bypassed or overruled but they are rarely used. Generally, members who have been in Congress longer have greater seniority and therefore greater power.