 Complete the following phrase:  When Lithuania gained Vilnius as a result of the SovietLithuanian Mutual Assistance Treaty in October 1939, Landsbergis became the chief engineer of Vilnius. He helped Balys Dvarionas organizing the Lithuanian National Symphony Orchestra in 1940 and prepared a project for a 1,200-seat opera and ballet theater it was not constructed. After Lithuania was occupied by the Soviet Union in June 1940, Landsbergis became the chief architect of Vilnius. When 