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Half-Life: Opposing Force Tham khảo|url=
(trợ giúp). Eurogamer. Truy cập ngày 20 tháng 11 năm 2008.|publisher=
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Half-Life: Opposing Force Tham khảoLiên quan
Half-Life: Alyx Half-Life: Opposing Force Half-Life: Blue Shift Half-Life (loạt trò chơi) Half-Life Half-Life 2: Episode Two Half-Life 2: Episode One Half-Life 2Tài liệu tham khảo
WikiPedia: Half-Life: Opposing Force http://www.computerandvideogames.com/article.php?i... http://www.computerandvideogames.com/article.php?i... http://www.computerandvideogames.com/article.php?i... http://eforall.gamepro.com/article/reviews/3231/ha... http://www.gamerankings.com/htmlpages2/149551.asp?... http://www.gamespot.com/reviews/half-life-opposing... http://ep1.half-life2.com/story.php http://uk.pc.ign.com/articles/067/067720p1.html http://uk.pc.ign.com/articles/068/068711p1.html http://uk.pc.ign.com/articles/078/078919p1.html