Simplify the following text for a Grade 9 native English-speaking person.
Original: The agreement affirmed Mongolia 's complete autonomy in internal matters and Russian privileges in Mongolia , at the same time formally recognized China 's suzerainty over the country .
Simplified: The agreement stated that Mongolia 's was completely autonomus in internal matters and that Russia had certain privileges in Mongolia . At the same time it said that Mongolia was in facr a part of China .