Why does the oceanic crust sink beneath the continental crust at the subduction zone

oceanic crust sinks because it is denser and has higher specific gravity than the more silicon aluminum enriched continental crust. What drives substitution is convection and conduction in outer core of earth, that heat , only a small part of which is due radioactive isotopes, has to make it's way to Earth's surface by both conduction and convection. Iron and nickel o have the highest specific gravities of the 10 most common elements in the Milky Way Galaxy. This is why oceanic crust sinks and is subducted continental crust has to have a lot more force applied before it inks, because it doesn't want to sink.

b is the right answer for this question.