code: def backbone(model_name: str, **kwargs):
      model_list = [
          "slowfast50",
          "slowfast101",
          "slowfast152",
          "slowfast200",
      ]
      if model_name == "slowfast50":
          model = SlowFast(Bottleneck, [3, 4, 6, 3], **kwargs)
      elif model_name == "slowfast101":
          model = SlowFast(Bottleneck, [3, 4, 23, 3], **kwargs)
      elif model_name == "slowfast152":
          model = SlowFast(Bottleneck, [3, 8, 36, 3], **kwargs)
      elif model_name == "slowfast200":
          model = SlowFast(Bottleneck, [3, 24, 36, 3], **kwargs)
      else:
          raise ValueError(
              f"Expected element in {model_list} but got: {model_name}."
          )
      return model
  
file_path: towhee/towhee/models/acar_net/backbone.py
imports: import torch
  from torch import nn
label_desc: Use image node_id 1 for calling a global function with example usage: backbone(model_name) and returns: model