Mr.Li has some trouble sleeping so drinking a glass of milk before going to bed every nig

问题补充：

Mr.Li has some trouble sleeping, so drinking a glass of milk before going to bed every night is his common

A. practice

B. knowledge

C. experience

D. duty

答案：

(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。