汇率是用外币表示的用于国际间结算的支付手段；外汇是两种货币的兑换比率。()
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What is NOT true about the scramjet engine？
A. It goes slower than a rocket．
B. It extracts oxygen from the air that flows through the engine．
C. It works only at speeds greater than five times the speed of sound．
D. It doesn’t carry its own 0xygen supply．
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