According to article 2 of the constitution, what body of government checks the legislative authority of congress

The answer to this question is Congress.
The article II of the constitution written that the president had the power to veto the law/regulations that is passed by the congress and the congress also has the power to override the veto made by president
This power give both the congress and president to watch over each other and limit their power in the government.

They are called independent

Americans often speak of their country as one of several large regions.  these regions are cultural units rather than governmental units --  formed by history and geography and shaped by the economics, literature and folkways that all the parts of a region share. what makes one region different from another? a region's multicultural heritage as well as distinct demographic characteristics like age and occupation make regions different and special. within several regions, language is used differently and there are strong dialects. there are also differences in outlook and attitude based on geography.