def createTransactionLookupConnector(chain=Chain.bitcoin_mainnet, options=None):
    """
    :param chain: which chain, supported values are testnet and mainnet
    :return: connector for looking up transactions
    """
    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)
:param chain: which chain, supported values are testnet and mainnet
    :return: connector for looking up transactions