How do ocean ridges and deep sea trenches support the theory of seafloor spreading?

Mid Oceanic Ridge (MOR) to Deep-Oceanic trench

Explanation:

As the plate tectonic theory is a continuous process, so at some places, divergent plate movement takes place whereas at other places, convergent plate movement takes place. So from that context we can conclude that initially two plates moves apart from each other, and this plates then collides with the other nearby plates, thereby the heavier one gets subducted beneath the other, forming a deep sea trench.

a "theory" a suggestion that is not 100 % accurate, or a figure. some people say its a theory because they of all the passed theory's about one subject. it depends sometimes theory might be accurate and sometimes they are.