. . "(1) an alkyl group which may be substituted with a halogen atom such as a fluorine atom, a chlorine atom and a bromine atom, (2) a phenyl group which may be substituted with aforementioned substituent or substituents, or (3) an aralkyl group which may be substituted with aforementioned substituent or substituents, Z stands for an oxygen atom or a sulfur atom, n stands for an integer of 0 to 2, X s" . . .