試題詳解

68.下圖中當R1、R2、R3及R4為下列何種取代基時，此結構為doxycycline？ 
(A)R1＝OH，R2＝CH3，R3＝R4＝H
(B)R1＝R3＝OH，R2＝CH3，R4＝H
(C)R1＝R4＝H，R2＝CH3，R3＝OH
(D)R1＝R2＝R3＝H，R4＝N(CH3)2