 Complete the following phrase:  1968 turned out to be a turning point in the history of Formula One, in terms of technicalities and safety. Wings were used on Formula One cars and aerodynamics really played a part in terms of the cars performance, and 5 Grand Prix drivers were killed in this year  including Jim Clark, Mike Spence, Jo Schlesser and Ludovico Scarfiotti  Clark at a Formula 2 race at Hockenheim in a Lotus in April, Spence during practice for the Indianapolis 500 in a Lotus in May, Scarfiotti during a hillclimb event in Germany driving a Porsche sportscar in June, and Schlesser during the 