Answer:
Subducts
Step-by-step explanation:
According to Merriam Webster and TheFreeDictionary, the definition of subduct is "A geologic process in which one edge of one crustal plate is forced below the edge of another." Since this sentence indicates that an oceanic plate sinks under the continental plate, therefore I believe the fill-in-the-blank word would be 'subducts' or a similar word.