Which of the following is NOT MENTIONED in the passage?

A.New techniques are continually developed and new machines invented for undersea exploration. B.If not well built, a submersible is most likely to get crushed in deep water. C.A submersible, when manned looks very much like a spaceship. D.In certain respects undersea exploration is often faced with the same problem as space travel is.

时间:2023-10-07 16:10:07

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