Final answer:
At a transform boundary, the plates slide past each other horizontally, which often results in earthquakes due to the movement along faults.
Step-by-step explanation:
The correct answer to the question regarding what happens at a transform boundary when the two plates interact is that the plates slide past each other horizontally, causing earthquakes. This occurrence is typical of transform boundaries, where there is no creation of new crust or subduction of one plate beneath another. Instead, the plates simply move sideways relative to each other along faults, leading to the potential for seismic activity as they release stored energy.