题目内容
What is America's most important food crop?
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Service industries account for about ___ of the US gross domestic product.
The westward expansion is a demonstration of American ___.
With the arrival of the 20th century, the US became increasingly urbanized, particulary in the ___ cities.
As the world's leading maker of industrial goods, the US now produces around ___ of the world's industrial products according to the text book.
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