More fundamentally, democracy lets people speak their minds and shape their own and their children’s futures. That so many people in so many different parts of the world are prepared to risk so much for this idea is testimony to its enduring appeal.

请问：That so many people in so many different parts of the world are prepared to risk so much for this idea 这是主语从句，为什么用 that 来引导？

【答】不错，这是主语从句。不过你这个问题，问得有点怪。

我想问问你：一个表示陈述意义的句子，充当了主语从句（或者其他名词性从句，如：宾语从句，表语从句，同位语从句）时，如果不用that引导，那么，应该用什么词引导呢？