langchain/indexes/vectorstore.py/VectorStoreIndexWrapper/query
class VectorStoreIndexWrapper:    def query(
        self, question: str, llm: Optional[BaseLanguageModel] = None, **kwargs: Any
    ) -> str:
        """Query the vectorstore."""
        llm = llm or OpenAI(temperature=0)
        chain = RetrievalQA.from_chain_type(
            llm, retriever=self.vectorstore.as_retriever(), **kwargs
        )
        return chain.run(question)