单项选择题

According to the text, the fundamental cause of the ice ages is ______.

A．periodic changes in the earth's orbit around the sun
B．fossil remains of one-celled animals
C．alternating cold and warm seasons
D．changes in distance of the earth from the sun

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热门试题

单项选择题

One reason that children are unable to resist giving personal information on the Intemet is ______.

A．it is presented in connection with entertainment
B．they do not know that the information is going to be read by someone
C．they feel they must follow an adult's orders
D．due to their inability to distinguish an advertisement from a non-advertisement

单项选择题

The first paragraph of the text deals mainly with the earth atmosphere's ______.

A．sheltering effect
B．reviving effect
C．invigorating effect
D．cleansing effect