<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def etree_to_string(tree):
 """Creates string from lxml.etree.ElementTree with XML declaration and UTF-8 encoding. :param tree: the instance of ElementTree :return: the string of XML. """

        buff = BytesIO()
        tree.write(buff, xml_declaration=True, encoding='UTF-8')
        return buff.getvalue()