单项选择题

Sedimentary rocks cover much of the Earth’s surface, but they are often hidden by a thin veneer of soil.

A．concealed
B．eroded
C．protected
D．softened
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单项选择题
Compared with large aircraft, small airplanes are not as streamlined and hence are less efficient.
A．at a glance
B．to a measurable degree
C．in most cases
D．as a result
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