Read this: Under the 1995–2004 National Hockey League collective bargaining agreement, teams were limited to nine preseason games. From 1975 to 1991, NHL teams sometimes played exhibition games against teams from the Soviet Union in the Super Series, and in 1978, played against World Hockey Association teams also in preseason training. Like the NFL, the NHL sometimes schedules exhibition games for cities without their own NHL teams, often at a club's minor league affiliate (e.g. Carolina Hurricanes games at Time Warner Cable Arena in Charlotte, home of their AHL affiliate; Los Angeles Kings games at Citizens Business Bank Arena in Ontario, California, home of their ECHL affiliate; Montreal Canadiens games at Colisée Pepsi in Quebec City, which has no pro hockey but used to have an NHL team until 1995; Washington Capitals at 1st Mariner Arena in the Baltimore Hockey Classic; various Western Canada teams at Credit Union Centre in Saskatoon, a potential NHL expansion venue). Since the 2000s, some preseason games have been played in Europe against European teams, as part of the NHL Challenge and NHL Premiere series. In addition to the standard preseason, there also exist prospect tournaments such as the Vancouver Canucks' YoungStars tournament and the Detroit Red Wings' training camp, in which NHL teams' younger prospects face off against each other under their parent club's banner.
Now answer this question, if there is an answer (If it cannot be answered, return "unanswerable"): In what year did the NHL play against World Hockey Association teams?
1978