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【单选题】
蝶泳打水产生推进力主要是在(）。
A.
向下打水
B.
向下打水和向上打腿均不产生推进力
C.
向上打水
D.
向上打水和向下打水两阶段
参考答案：
参考解析：
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【单选题】It has been necessary to refer repeatedly to the effects of the two world wars in promoting all kinds of innovation. It should be (62) also that technological innovations have (63) the character of wa...
A.
observed
B.
notified
C.
commented
D.
detected