Mr.Li has some trouble sleeping, so drinking a glass of milk before going to bed every night is his mon
A. practice
B. knowledge
C. experience
D. duty
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(答案→)A. practice
B. knowledge
C. experience
D. duty
解析：考查名词辨析：A、practice练习，做法，B、knowledge知识，C、experience经验，D、duty责任，值日，句意：李先生睡觉有困难，所以每天晚上睡觉前喝杯牛奶是他的惯例。Commom practice是“惯例”，选A。