例句：
The problem is that there are often no signs until it is too late，making it difficult to avoid．
问题总是在它没法避开时，才会出现一些迹象．
根据句式结构The problem（主语） is that there are often no signs until it is too late（表语从句），_______it difficult to avoid（结果状语），因为迹象出现的太晚，所以使得避开很难，这是一个必然的结果
考查现在分词做结果状语．结果状语分意料之中和意料之外两种，前者用doing，后者用to do．
由 that 引导的表语从句 (that 有时可以省略)。The problem is that most of the students think their uniforms are ugly. 问题是大部分学生认为他们的校服很难看。The trouble was that the enemy destroyed all the bridges. 麻烦的是敌人炸毁了所有的桥梁。
The problem is that we haven’t got enough money. 问题就是我们还没有足够多的钱。(that 从句用作表语)
the problem is that是典型的表语从句，详解如下。
表语从句（Predicative Clause）就是用一个句子作为表语。表语（Predicative Clause）的作用是用来说明主语是什么或者怎么样，可以由名词、形容词或相当于名词或形容词的词或短语充当，和连系动词一起构成谓语。要注意，表语从句属于名词性从句，只是表语的其中一种情况——由名词充当表语。
