正解:A
In the context of NETCONF, which is an XML-based protocol used for network configuration, the most efficient way to reduce the amount of data returned by the NETCONF server is to use an XML filter. By creating an XML filter as a string, you can specify the exact configuration data you need, such as the interface's configuration in this case. When this filter is passed to the get_config() method as an argument, the NETCONF server will only return the data that matches the filter criteria, thus reducing the amount of data sent to the NETCONF client.