问一个OG12的题（状语从句里主谓的省略问题）

kakadinho

OG 12th-14

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（A）
(E) appear as dark spots on the Sun’s surface, which have never been sighted on

偶对答案A没有异议，也做对了。但是看OG关于C \ D的解释(如下)，发现although不能省略后面的主谓，就算这题里从句主语显然就是主句的主语：
C.Although typically introduces a subordinate clause, which has a subject and a verb, but here there is no subject and sighted is not a complete verb



D.Although usually introduce a subordinate clause, but there is no subject of the clause and having been sighted is not a complete verb phrase
这好像和刘振民和白勇的说法有些出入。如果说OG就用这个就排除了，这应该是一个correctness的错误吧。
刘振民说：如果although/when/if... 之类的引导的状语从句，后面从句主语如果和主句一致，且同时谓语动词是be， 就可以省略主谓。

是否可以这样理解： 以上构成省略的be指的是实义动词be， 而不是助动词be，而C\D选项中 sighted 和 having been sighted 就算前面有个be省略，那个be也是助动词，所以不能省略，所以错。（何况be having been sighted也绝对awkward）

期待大牛们解释。我也查了历史讨论，但好像没有人给出明确的理解。以上观点也有被讨论过但无人证实。
本来想本着相对最优就放过这个题了，反正A也对称，但是看到OG的官方解释，省略错误竟然是C、D的唯一排除理由，所以还希望搞懂。

kakadinho

没人搭理我，自己顶先~

sheikh239

呃 是刘振民白勇出题考你还是GMAC出题考你...

所以，想清楚这个问题，速速弃暗投明吧，孩子

这个省略的问题我当初看lzm的时候也深究过，结论和你一样，可惜毫无实战作用。
那些书，看完就丢，开始的时候复习一下而已。