We firmly believe that ___ the new examination system comes into existence, completely new situations will arise.

A. considering    B. supposed      C. providing       D. given

答案是C 为什么supposed不行呢 B和C之间的区别在哪里呢？

 【答】supposed 不可以用作连词引导条件状语从句。

   以下内容摘自《刘毅英语语法宝典》p.522，可以解答你的问题：

   suppose (that)/supposing (that)/ provided (that)/ providing (that)（= if)(如果）

    Suppose (that) I were to help you, would you try it again? 如果我帮助你，你愿不愿再试一次？【suppose 比 suppose that 常用】

    Suppose I were a bird, I would fly to you. 如果我是只鸟，我会飞到你身边。

    Suppose I meet him, what shall I tell him? 如果我遇见了他，我该告诉他什么呢？

    Supposing (that) you died,what would become of your children? 如果你死了，你的孩子会变成什么样呢？

    Supposing (that) It rains tomorrow, what shall we do? 如果明天下雨了，我们怎么办？

    We shall start at three o'clock provided (that) the car is ready then.如果汽车在那时候准备妥当，我们将在3点启程。

    I don't mind lending you the money provided (that) you pay it back within a year. 如果你能在一年之内还我，我就不介意把钱借你。

    I will come providing (that) I have time.如果有时间，我会来的。

    I will go providing my expenses are paid.如果我的开销有人付，我就去。

   【providing 比 providing that 常用】

    He will go providing it doesn't rain. 如果不下雨，他就会去。

   【注】say 也可以代替 suppose 。

         Suppose you were in his place, would you do it?

         Say you were in his place, would you do it?

        （假如你站在他的立场，你会做那件事吗？）

虽然这里面的每个选项都很别扭，但相比而言只有C能够选入。另外，这种句子基本上是国内学校老师为考试而编造的一种生硬的句子。

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就算选项里有suppose/supposing，也是不对的，这人词表示条件是假想的，假设的。这个时候是一个假想的语境，而你前面是we firmly believe，形成了语境冲突，故不能入选。