The movement of tectonic plates in two different locations is shown below:

two blocks labeled location a and location b are shown. at location a the top layer of the block shows two horizontal arrows pointing towards each other. the portion of this block on the right is shown moving down. the block labeled b shows two horizontal arrows pointing away from each other. a vertical gap is seen in the middle

which statement is most likely true?

subduction occurs in both locations.
seafloor spreading occurs in both locations.
an earthquake may occur in location a and subduction occurs in location b.
subduction occurs in location a and a volcanic eruption may occur in location b.