单项选择题

This passage is mainly about______.

A．the beginnings of oceanography
B．the laying of the first undersea cable
C．the investigation of ocean depths
D．the early intercontinental communications

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单项选择题

The aim of the voyages Maury was responsible for in the 1840s was______.

A．to make some sounding experiments in the oceans
B．to collect samples of sea plants and animals
C．to estimate the length of cable that was needed
D．to measure the depth of the two oceans

单项选择题

Defied in the 3rd paragraph probably means ______.

A．doubted
B．gave proof to
C．challenged
D．agreed to