①美元兑换人民币的汇率升高 ②美元兑换人民币的汇率跌落
③美元兑换人民币增多 ④人民币兑换美元增多
A:②④
B:③④
C:①③
D:①②
在极坐标系中,点A(1,π)到直线ρcosθ=2的距离是( )
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