code: def createTransactionLookupConnector(chain=Chain.bitcoin_mainnet, options=None):
      
      if chain == Chain.mockchain or chain == Chain.bitcoin_regtest:
          return MockConnector(chain)
      elif chain.blockchain_type == BlockchainType.ethereum:
          if options and 'etherscan_api_token' in options:
              etherscan_api_token = options['etherscan_api_token']
          else:
              etherscan_api_token = ''
          return EtherscanConnector(chain, etherscan_api_token)
      return FallbackConnector(chain)
docs: :param chain: which chain, supported values are testnet and mainnet
      :return: connector for looking up transactions