People planning trips home used to believe that only through the railway’s telephone ticket hotline get their tickets efficiently.
A. they may
B. could they
C. shall they
D. they would
网友回答
A. they may
(答案→)B. could they
C. shall they
D. they would
解析：在句首的only如果后面跟了副词、介词短语或从句等状语，则主句用倒装结构。如only后跟的是主语，就不用倒装结构了。例如：
Only when the war was over in 1918 was he able to get back to work．
Only the teachers are allowed to use the room．（不倒装）
句意：计划回家的人们过去认为只有通过铁路电话订票热线才能有效地买到票。四个选项看，only的倒装，必须用于句首，在宾从中的句首，也需要部分倒装