 Complete the following phrase:  Christie took his examen artium in 1935, and attended the Technische College of Berlin from 1935 to 1937 and Hærens Flyveskole from 1937 to 1939. As World War II broke out, Christie, with the rank of sergeant, was called to Sola Airport as a member of Norways neutrality guard. However the airport was attacked by Germany on 9 April 1940 and fighting ensued. The Norwegians lost the battle, but Christie managed to retreat to the inner country. His group was involved in 