Which of the earth's layers is represented by the number four (4) on the image above?

1. being the crust (obviously)
4. being the last/inside

Brand c i think that should be it

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