Hanoi, in the hours before National Day celebration The capital city becomes serene as Vietnam is ready for the 70th anniversary of its National Day    A billboard recites the national motto "Independence - Freedom - Happiness." Flags and balloons are seen near the President Ho Chi Minh Mausoleum.    Many local streets become quiet on Tuesday. Hanoi's authorities will close 40 streets from 9 p.m. on Tuesday to Wednesday noon for the celebration.   An old man looking photos displayed at an outdoor exhibition that features nearly 200 photos of Hanoi during years before 1946 in Hoan Kiem District. It also displays photos of Vietnam's first president Ho Chi Minh after the historic day.   National flags are seen along a small Hanoi alley.    Workers take care of a public garden before the celebration.   Thanh Nien News