WHO HAS BIG BRAINS? not me... so please help? What is isostasy dependent on a balance between?

A.)the downward push of the mantle and the upward push of the continents

B.)The downward push of the ocean floor and upward push of the continents

C.)The downward push of the continents and upward push of the mantle

D.)The downward push of the ocean floor and upward push of the mantle