单项选择题

In ancient times, some catastrophic extinction of species occurred ______, but such catastrophes were comparatively rare.

A．sequentially
B．repeatedly
C．naturally
D．intentionally
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单项选择题
The manager threw a party ______ the group of computer experts from the United States.
A．in honor of
B．in favor of
C．in welcome of
D．in celebration of
单项选择题
In a barter economy, finding somebody who wanted to trade his old car ______ a sailboat might not always be an easy task.
A．in terms of
B．by auction for
C．by way of
D．in exchange for
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