这句英语句子成分怎么划分？

Why is making mistakes such a great barrier to your starting speaking English?
1. making mistakes 主语
2. is such a great barrier谓语+ 表语
3. to your sarting speaking English 定语， 修饰barrier.
4. why状语。

主语：making mistakes
谓语动词 is
宾语：such a great barrier
to介词表目的
整句意思是：为什么犯错误是这样一个阻碍你开始学口语英语的障碍呢？