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参考解析：
刷刷题刷刷变学霸
举一反三
【单选题】It is hard to track the blue whale, the ocean’’s largest creature, which has almost been killed off by commercial whaling and is now listed as an endangered species. Attaching radio devices to it is d...
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
【单选题】医生在诊病时常使用听诊器，听诊器的工作原理是（ ）。
A.
使心脏振动的振幅增加，响度增大
B.
改变心跳的频率，使音调变调
C.
改变心跳的音色，使声音好听些
D.
减小声音传播过程中的能量损耗
【单选题】已知，Rt△ABC中，∠C=90°，AD平分∠BAC交BC于D，若BC=32，且BD：CD=9：7，则D到AB的距离为（ ）
A.
18
B.
16
C.
14
D.
12