1) what happens when 2 continental plates collide? 2) what happens to the oceanic crust that subject under the oceanic crust?

The answer is B hope it helps :)

1). Neither plate sinks, instead, the two plates slowly fold and pile up on top of each other, forming mountains
2). An oceanic plate collides with a continental plate. Oceanic crust tends to be denser and thinner than continental crust, so the denser oceanic crust gets bent and pulled under, or subducted, beneath the lighter and thicker continental crust. This forms what is called a subduction zone.

Answer(a); // soil salinization and waterlogging;