He spoke English slowly and clearly ___ ,because they are all freshmen.

问题描述:

He spoke English slowly and clearly ___ ,because they are all freshmen.
选项的正确答案是so as to be understood 而还有一个选项是 to be understood
不是说to be 不定式可以表目的的吗?为什么 to be understood不可以选?

so as 是以便的意思.
他说英语又慢又清楚,以便他讲的话能够被(他们)听懂,因为他们都是新生.
to be understood 不能表示目的