[求助]OG11-9中AS的用法问题

9.Sunspots, vortices of gas associated with strong electromagnetic activity, are visible as dark spots on the surface of the Sun but have never been sighted on the Sun's poles or equator.
(A) are visible as dark spots on the surface of the Sun but have never been sighted on
(B) are visible as dark spots that never have been sighted on the surface of the Sun
(C) appear on the surface of the Sun as dark spots although never sighted at
(D) appear as dark spots on the surface of the Sun, although never having been sighted at
(E) appear as dark spots on the Sun's surface, which have never been sighted on
正确选项是A

看了很多讨论此题的帖子，大家更多的是关心Although省略的问题，但是很少有讨论AS的问题的，所以发新帖求助这里AS的用法，按照ETS的解释AS作为连词引导从句，LIKE作为介词引导短语，此处明显不是主谓结构的从句，为什么AS还是正确的呢？

PS：当然如果没有LIKE的选项可选，我也没什么问题，但是一旦出现一条LIKE的选项我们该如何排除呢？或者说这里AS为什么对？换成LIKE还对么？希望NN们能解释一下，谢谢啦：）

as也能作介词.解释为"作为";

like用于物物对比.