What airmass and source regions provide the greatest amount of moisture to the eastern and central United States

The answer is a since the earth has different layers

Answer primary waves;

The us is first  the  u.s. economy  remains the  largest in the world  in terms of nominal  gdp. however, the  u.s. economy  loses its spot as the number one  economy  to china when  measured  in terms of  gdp  based on ppp. in these terms, china's  gdp  is $23.19 trillion exceeds the  u.s. gdp  of $19.42 trillion

Don't depend on this but logically i think c