 Complete the following phrase:  The Prague Canoeing Centre is one of the most frequently used venues for international canoe slalom competition. Built in 1983 in Czechoslovakia, it diverts water around a dam at Troja on the Vltava river in Prague. Its two unique features are its use of car and truck tires as flow diverters and its shallow slope, closer to 1 than the usual nearly 2 for such venues. Despite these characteristics, the Troja facility has hosted ten World Cup races and one World Championship in the 21 years 19922012, and the 