code: def _get_checked_sentence(self, knowledge_no_title):
      # choose a sentence from the retrieved knowledge using a
      # Transformer-based ranking model; the downstream dialogue model may
      # or may not make use of this chosen sentence
      selector_obs = self._format_selector_observation(
          knowledge_no_title,
          episode_done=self.observation.get("episode_done", False),
      )
  
      self.selector.observe(selector_obs)
      chosen_sentence_act = self.selector.act()
      cands = chosen_sentence_act.get("text_candidates", [])
      if not cands:
          return ""
  
      for cand in cands:
          if cand not in self.checked_sentence_history:
              self.checked_sentence_history.append(cand)
              return cand
  
      # return best prediction
      return cands[0]
  
imports: from typing import Optional
  from parlai.core.params import ParlaiParser
  from parlai.core.opt import Opt
  from parlai.core.agents import Agent, create_agent, create_agent_from_shared
  from parlai.core.torch_ranker_agent import TorchRankerAgent
  from parlai.tasks.wizard_of_wikipedia.agents import TOKEN_KNOWLEDGE
  from parlai.zoo.wizard_of_wikipedia.knowledge_retriever import download
  import json
  import os
label_desc: Use image node_id 11 for calling the KnowledgeRetrieverAgent obj's underlying member method code with example usage: obj._get_checked_sentence(knowledge_no_title) and returns: cands, str, cand