Given the task definition and input, reply with output. In this task, you will be presented with a context from an academic paper and a question separated with a
. You have to answer the question based on the context.

In order to find the object type, SimplerVoice, first, builds an ontology-based knowledge tree. We propose to use 2 methods to generate the suitable verbs for the target object: heuristics-based, and n-grams model.
Question: Which model do they use to generate key messages?
ontology-based knowledge tree heuristics-based n-grams model