Q31

In the sixteenth century, the push for greater precision in measuring time was (not, like more recently, motivated by complicated philosophical questions about the nature of matter and the universe, but the practical matters of navigation):sailors simply needed more highly accurate timepieces in order to compute their longitude from the positions of the stars.

(E) motivated not by complicated philosophical questions about the nature of matter and the universe, as has been the case more recently, but by the practical matters of navigation

(E)是答案没问题，但（E）中: , as has been the case more recently, 在语法上如何透彻理解呢？ as 是什么词性？ 为何意呢？ 是代词？代什么？