a single middle school (unless the team is composed entirely of home schooled students). Only four students play at any one time, while the fifth is designated as the "alternate." Substitutions may be made during the two-minute "halftime" and between rounds. Two teams compete against each other in each match. Each match has exactly 25 questions (that is, 25 toss-ups and 25 bonuses in corresponding categories). The match is over when all the toss-up questions have been read, or after two eight-minute halves have elapsed (ten-minute at the national competition), whichever occurs first. The team with the most points at this time is the winner. Toss-ups Every match begins with a toss-up question. The moderator announces the subject of the question (see "Subject Areas" above), as well as its type (Multiple Choice or Short Answer). Once the moderator completes the reading of the question, students have five seconds to buzz in and give an answer. Students may buzz in at any time after the category has been read — there is no need to wait for the moderator to finish. However, there is a penalty for interrupting the moderator and giving an incorrect answer. Once a student from a team has buzzed in, that team may not buzz in again on that question. Conferring between members of a team is not allowed on toss-up questions; if conferring occurs on a question, the team is disqualified from answering that question. The rules regarding conferring are typically very strict: excessive noise, eye contact, or even noticeable shifts in position can be considered conferring, as they convey information to teammates. The moderator rules an answer given by a student correct or incorrect. On short answer questions, if the answer given differs from the official one, the moderator uses his or her judgment to make a ruling (which is subject to challenge by the competitors). On multiple-choice questions, the answer given by the student is only correct if it matches the official answer exactly. Alternatively, the student may give the letter choice that corresponds to the correct answer. The letters W, X, Y and Z are used in lieu of A, B, C and D to avoid confusion between similar-sounding letters. The decision to require multiple-choice answers to be exact has been a controversial one, but experience has shown that it is the best way to avoid complicated disputes during matches. Bonuses If a