(1)BrCH:CH2Br+Mg EtO? (2)BrCHzCH2CHaBr+Mg EtO? (3)BrCHaCH2CH.CH2Br+Mg EtO2 ④CH,CH=CHCHaBr+-MgTH、? (2) BrCH2CH2CH2Br + Mg ? Et2O (1) BrCH2CH2Br + Mg ? Et2O (3) BrCH2CH2CH2CH2Br + Mg ? Et2O (4) CH3CH CHCH2Br + Mg ? THF