Which one of the following simple ethers cannot prepared by williamson synthesis in good yields

C6H5-O-CH3.....Anisole.....mixed ether; C6H5-O-C2H5.....Phenetole.....mixed ether; C2H5-O-C2H5.....diethyl ether.....simple ether; C2H5O-Na++C2H5Cl→C2H5-O-C2H5+NaCl ....SN2; Ethyl chloride is a 10 R-X....good yield of ether is obtained; But to prepare diphenyl ether, the starting materials must be, C6H5O-Na++C6H5Cl....C6H5Cl is non reactive towards nucleophilic substitution due to resonance; Diphenyl ether cannot be prepared by williamson's synthesis;