18-10AS 阅读 Q20

提问最后一段的injection的暗喻的目的是什么。原文最后一段强调黑人的贡献：we are the injection, the shot in the arm, that has kept America and its gotten principles alive in the fat and corrupt years. 所以对应到D选项，强调黑人的贡献。A选项的个人牺牲没有；B选项的美国人和理想的对等没有；C选项的danger没有。