1. Olga lives in Russia.
2. The deepest lake in the world is Lake Baikal.
3. The longest river in the world is Nile.
4. The most famous Moscow theatre is a Bolshoy Theatre.
5. America is a continent and USA is a country.
6. I also went to a St. Basils Cathedral.
7. The moon goes around the sun.
Примечание: С географическими названиями артикль a и the не ставятся, так как это исключения.