 Complete the following phrase:  After a one-year trial run in Drammen in 1939 the first trolleybus route in Oslo opened in 1940. This was line 17, a 1.6 km feeding line at Rodeløkka. This line only used one bus, that didnt run on Sundays so it could be maintained. Then came World War II with fuel shortage, resulting in the trolleybus being quite popular, as Norway had ample electricity. But there were other problems, including material shortage and the fear of the 