In order to ensure that he can attend the meeting,I called him up in advance.to在这里不是介词吗?

题目

In order to ensure that he can attend the meeting,I called him up in advance.to在这里不是介词吗?
为什么ensure后面不加ing?

答案

因为in order to 后要接动词原形,即 to + 动原 构成不定式.