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参考答案：
参考解析：
刷刷题刷刷变学霸
举一反三
【单选题】As in the field of space travel, so in undersea exploration new technologies continue to appear. They share a number of similarities with each other—as well as some important differences. Manned subme...
A.
the ocean depths
B.
the communication problem
C.
the movement of waves
D.
the problem of vacuum