## destructor
dstrc = Destructor()
    finest_symdis(self, str0, opt="None", return_flag=False):
        """
        If return_flag is True, return whether the string given is that type
        that you want to know; otherwise return the finest-grained term of
        that string(word)
        :param str0: term word given
        :param opt: filter option: "None": none is filtered; "Symptom": only symptom kept
        "Disease": only disease kept
        :param return_flag: control the return type of the function
        :return: defined by return_flag
        """