单项选择题

"Defied" in the 5th paragraph probably means （）

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

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单项选择题

The aim of voyages Maury encouraged in the 1840s was （）

A．to make some sound experiments in the oceans
B．to collect samples of sea plants animals
C．to estimate the length of cable that was to be made
D．to measure the depths of two oceans

单项选择题

How many different forms of communication are mentioned here （）

A．5.
B．7.
C．9.
D．3.