Before mailing it in, please make sure that you enclose your reference letters
with your resume.
make是SVOC
that you enclose your reference letters with your resume是名詞子句
sure是補語
書中的解釋是O太長所以掉到後面，但是這種狀況不是應該用虛主詞it嗎?
如下面這樣
please make it sure that you enclose your reference letters with your resume.
請問這句話的文法是如何呢 ?謝謝^^