单项选择题

The passage is mainly about ______.

A．the features of volcanic activities
B．the importance of the theory about drifting plate
C．the significance of hot spots in geophysical studies
D．the process of the formation of volcanoes

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单项选择题

The hot spot theory may' prove useful in explaining ______.

A．the structure of the African plates
B．the revival of dead volcanoes
C．the mobility of the continents
D．the formation of new oceans

单项选择题

That Africa and South America were once joined can be deduced front the fact that ______.

A．the two continents are still moving in opposite directions
B．they have been found to share certain geological features
C．the African plates has been stable for 30 million years
D．over 100 hot spots are scattered all around the globe