請問這個based是什麼語法?爲什麼前面是過去式後面的investigate用一般現在時?

題目：

請問這個based是什麼語法?爲什麼前面是過去式後面的investigate用一般現在時?
Based on some qualitative and quantitative analyses,this
paper investigates the method of measuring external costs of
congestion.

解答：

Based on不是過去式,而是被動式,它與全句的主語this paper構成被動關係,前面省略了being（即開頭爲being based on...）.
這是非謂語動詞（或者說獨立主格）的一種用法.
把這句話拆成兩句的話,就是：
This paper is based on some qualitative and quantitative analyses.
This paper investigates the method of measuring external costs of congestion.
不知道是不是說清楚了^_^