单项选择题

The author compare the ocean bottom to a "frontier" in paragraph 1 because it______.

A．is a quite promising place.
B．is out of the understanding of many scientists.
C．attracts courageous explorers.
D．is an unknown research area to the scientists.

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单项选择题

Which of the following is true of the Glomar Challenger

A．It is a type of submarine made especially for a project.
B．It is as ongoing project to explore the earth.
C．It provides such strong evidence that all earth scientists agree on the theories of plate tectonics and continental drift.
D．It makes great contribution to the understanding of the earth's structure.

单项选择题

Tire author's attitude towards the research of ocean bottom might be best summarize as one of______.

A．optimistic.
B．indifferent.
C．impartial.
D．critical.