The deep-sea listening system makes use of ______
A.the sophisticated technology of focusing sounds under water
B.the capability of sound to travel at high speed
C.the unique property of layers of ocean water in transmitting sound
D.low-frequency sounds traveling across different layers of water
第3题
A. 西周已经进入了封建社会
B. B.西周的等级制度具有血缘性
C. C.宗法制与分封制互为表里
D. D.血统是西周等级制度的唯一标准
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