定语从句的有关问题

We believe that this is only an inevitable trend, but _________ will prove beneficial.

A. one B. ones C. the one D. one that

这题选D，定语从句，但为何有一个but连词呢？不是应该后面跟完整的句子成分吗？

而且这个说是泛指，都有定语从句修饰了如何还是泛指呢？

We believe that this is only an inevitable trend, but one that will prove beneficial.

but 是表转折的并列连词，需要有，不可省略，以表示前后两个分句间的转折、对比关系。本句but 之后省略了it is，原句等于：

We believe that this is only an inevitable trend, but it is one that will prove beneficial.

这里one 仍然是泛指，即使有了定语从句修饰也是泛指。

We believe that this is only an inevitable trend, but it is one that will prove beneficial.

【翻译】大家觉得，这是一个不可防止未来发展趋势，但它将证明是有益的（一个趋势）。