33.Experts have been warning of the bealth risks caused by passive smoking
(A)at a time
(B)at one time
(C)for some time
(D)for the time

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詳解 (共 1 筆)

#1202169
本题考查固定短语。从句中have been warning 可知，应用for some time 一段时间，at a time 每次；at one time 曾经。
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