“Howdy!” This is a very informal abbreviation of “ How do you do？”（）
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English-speaking people usually greet each other in an（）way
A. formal
B. informal
C. casual
对里昂惕夫之谜有如下解释（）
A. 劳动效率的差异
B. 人力资本的差异
C. 自然资源因素被忽略
D. 要素密集型逆转发生
There are four very ______ seasons in my hometown（）
A. obvious
B. complete
C. beneficial
There is no need for us to use recycled paper.（）
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