Q:Given the following context:  Prior to the introduction of the current format of semifinals (deltävlingar) in 2002, the competition was usually a single live show. Under the current system, four semifinals are broadcast at 20:00 CET on consecutive Saturday nights. The semi-finals begin in early February, and seven songs compete in each show. Unlike in the final, no juries are used; televoting decides the results. The songs are performed live with telephone lines open for the first round of voting; two songs with the fewest votes do not qualify to the second round. The top five battle for a place in the final and Andra chansen round – the 1st and 2nd placed songs qualifying to the final, and the 3rd and 4th placed songs progressing to Andra chansen. Both finalists reprise their entries at the end of the broadcast. The organisation of a semi-final system for Melodifestivalen popularised televised heats at national Eurovision selections. A similar system was adopted by the Eurovision itself in 2004. The Second Chance round (Andra chansen) is the fifth heat in which the remaining four entries to the final are chosen. The third- and fourth-placed songs from each semi-final (eight songs in total) compete in the event. The first Second Chance round in 2002 had a panel of former winners decide the two finalists. Between 2003 and 2006, the semi-final performances were re-broadcast, and a round of voting narrowed the songs to three or four. Another round then determined the two finalists. The programme was broadcast on the Sunday afternoon after the fourth semi-final. It was held in a smaller venue than those that would have hosted the semi-finals—such as Berns Salonger in Stockholm, which hosted the Second Chance round in 2005. In 2007, the Second Chance round became a full semi-final, taking place in a venue comparable in size to those hosting the others. The expanded Second Chance takes place on a Saturday night, adding an extra week to the event's timetable. The format of voting also changed with the introduction of a knock-out system. The...  answer the following question:  What system pairs the eight songs off against each other?
A:
a knock-out system