问题补充:
单选题Itwasnotuntil1911,_______thefirstvitaminwasidentified,_______peoplerealizedtheimportanceofit.A.when; whichB.when; thatC.that; whichD.that; that
答案:
B解析考查定语从句和强调句型。定语从句When the first vitamin was identified修饰先行词1911,因为句子很完整,使用关系副词when.第二空与it was构成强调句型。句意:正是知道第一批维他命被识别出来的19,人们才意识到它的重要性。故B正确。