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The correct answer is A.
If an economy has a low output level, then a minor improvement in production has a large percentage impact. To illustrate, if you have a million dollars, presenting you with another dollar has a near-zero impact on your wealth. But, if you have only one dollar and are presented with another dollar, that is a one hundred percent improvement in your wealth. China has a very large population and, in the past, had comparatively little capital.