单选题
This region ______as the costliest place to do business.
A、
(A) often is referred
B、
(B) is often referred
C、
(C) is referred often to
D、
(D) is often referred to
【正确答案】
D
【答案解析】
Adverbs of indefinite frequency can appear between the auxiliary and the main verb. Choices (A), (B), and (C) are not appropriate positions for indefinite frequency adverbs.
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