最简单的方法是将it is\was及that去掉，并且剩余的部分组织起来，句子仍然能够组成完整的表达，并且成立，那么即为强调句，如若不能，否则不是强调句。
例如：All the members held a meeting in the room yesterday.
（强调a meeting ）It was a meeting that all the students held in the room yesterday.
（强调in the room ）It was in the room that all the students held a meeting yesterday.
（强调yesterday）It was yesterday that all the students held a meeting in the room.
It 作形式主语代替主语从句，主要是为了平衡句子结构，它是形式的主语而不是主语从句。主语从句的连词保持不变。它指向的强调句强调句子的一部分，不管强调的是什么，它都可以用作连接词。
主语从句：It is +形容词/名词/某些动词ed + that 从句。
扩展资料：
主语从句，即在复杂句中充当主语成分的句子，例如"That he finished writing the composition in such a short time surprised us all"，他在很短的时间内写完作文让我们都很惊讶。
此复合句主要描述的是某事让我们惊讶，某事就是该复合句的主语，因此“That he finished writing the composition in such a short time”便是该复合句的主语从句。
主语从句的时态不受主句时态的影响和限制
例如：
（1）That he finished writing the composition in such a short time surprised us all.
他在如此短的时间内写完作文使我们十分惊讶。
（2）Whether we will go for an outing tomorrow remains unknown.
我们明天是否会去郊游仍旧未知。
（3）Who will be our monitor hasn't been decided yet.
现在还没有决定谁会成为我们的班长。
（4）Whom we must study for is a question of great importance.
“我们为谁而学习”是个很重要的问题。
（5）What caused the accident remains unknown.
事故的起因是未知的。