The new suspension bridge ________ by the end of last month．
A.has been designed
B.had been designed
C.was designed
D.would be designed
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B解析在含有by引导的时间状语的句子里，谓语动词要用过去完成时：By the end of last year we had learned 2,000 new words．到去年年底，我们已经学习了2,000个生词．本题意为“悬挂桥已经于上月月底设计完成．”