Question

a subduction zone is formed...
when one tectonic plate
at type of divergent
sinks below another
plate boundary
at transform boundaries
at type of
convergent plate
boundary

Explanation:

Subduction zones form at convergent plate boundaries where one tectonic plate sinks (subducts) beneath another. Divergent boundaries create new crust, and transform boundaries involve sliding, not subduction.

Answer:

A. when one tectonic plate sinks below another