What Benefit Does the Size of the Earth Serve

What benefit does the size of the Earth serve? 

A)  Its size keeps it in orbit at a constant distance from the sun. 
B)  Its size provides enough gravitational mass to keep the light gaseous molecules in its atmosphere from flying off into space. 
C)  Its size keeps the iron-nickel core solid. 
D)  Its size prevents transfer of geothermal energy to the surface of the planet.