code: def conversation_to_fb_format(conversation):
      assert len(conversation) > 1
      lines = []
      for i in range(0, len(conversation), 2):
          if i + 1 < len(conversation):
              lines.append(
                  "%d %s\t%s"
                  % (i / 2 + 1, conversation[i], conversation[i + 1])
              )
          else:
              lines.append("%d %s" % (i / 2 + 1, conversation[i]))
      return "\n".join(lines)
  
imports: import parlai.core.build_data
  import glob
  import gzip
  import multiprocessing
  import os
  import re
  import sys
  import time
  import tqdm
  import xml.etree.ElementTree
  from parlai.core.build_data import DownloadableFile
  from parlai.utils.io import PathManager
label_desc: Use image node_id 9 for calling a global function with example usage: conversation_to_fb_format(conversation) and returns: str