白勇语法section3-29

irenelj78 · 发表于 2004-6-15 23:30:00

29. Once common throughout the Western plains, black-footed ferrets are thought to have declined in number as a result of the poisoning of prairie dogs, their prey.
(A) black-footed ferrets are thought to have declined in number as
(B) it is thought that the decline in number of black-footed ferrets is
(C) the decline in the number of black-footed ferrets is thought of as
(D) that black-footed ferrets have declined in their numbers is thought to be
(E) the numbers of the black-footed ferret are thought to have declined as

请问这道题中Once common是什莫意思啊？？

mariezhu · 发表于 2004-6-15 23:35:00

the forests are once common in the region

irenelj78 · 发表于 2004-6-15 23:49:00

thanks

白勇语法section3-29

白勇语法section3-29

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