The passage focuses on . We understand from the passage that the United States .

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问题 The passage focuses on ______.
We understand from the passage that the United States ______.

选项 A、is rich in low-grade aluminum-bearing ores
B、is short of aluminum-making techniques
C、has to import ninety percent of its annual need of aluminum
D、has to produce fifty percent of the world’s supply to meet its annual aluminum demand