As a child, he hoped to be a doctor. When he was fifteen,________, he changed his mind and wanted to be an engineer. A. however B. otherwise C.besides D.therefore 答案: A
咖啡酸()也叫3,4-二羟基桂皮酸,它存在于许多中药中,如野胡萝卜、光叶水苏等.咖啡酸有止血作用,对内脏的止血效果较好,毒性较小,还有镇咳、祛痰等疗效.下列关于咖啡酸的叙述不正确的是
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A.
咖啡酸能发生聚合、取代、酯化反应
B.
咖啡酸性质稳定,在空气中不易变质
C.
与咖啡酸分子式、官能团相同且苯环上取代基只有三个的同分异构体共有11种
D.
可用萃取的方法从野萝卜、光叶水苏中提取咖啡酸