天山3-31 as 的问题？

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？

我自己也顶！

我也帮你顶，顶到有NN来…

我不是NN，但AS用法好象以前讨论过。

AS在此是做关系代词，替代前面的整个句意。IN SHORT，ETS认为IT/THAT/WHICH都只能指代具体词而不能指代整个句意，但AS是个例外，既可以指代单词，词组，还可以指代整个句意。

tks ! make sense, 有道理，ETS老是变来变去搞得不知道他到底喜欢什么。

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.

(C)motivated not by complicated philosophical questions about the nature of matter and the universe, like they were more recently, but by the practical matters of navigation

(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

不好意思，PDF的东东偶不大会弄，只好只贴出有疑问的c选项，C和E只有这点差异，请问C错在哪里？

是like不能接句子吗？

请nn帮忙解答，谢谢

另外对E中的as has been the case more recently 还是很困惑阿

请NN指点