Slab Pull

Question 1

What is the process of slab pull?

Answer 1

At subduction boundary; one plate is denser than other plate.
Denser plate subducts underneath lighter plate into Benioff zone.
Edge of subducting plate is much colder and heavier than the mantle so it continues to sink pulling rest of plate along with it.

Question 2

Out of the 3 factors 
slab pull 
Ridge push 
Convection currents,
What’s the better option?

Answer 2

Slab pull