— Why didn’t they plete the task in time?— Because it was not until late afternoon _____ they began to solve the major problem．A.whenB.thatC.beforeD.which
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B解析考查强调句型。此题是一个含有not until 的强调句型，其结构为：it is/was + not until +其它+ that,下一个句子意思为：因为就是在下午晚些时候他们开始解决这个主要的问题。所以选B。