求问OG第17题，求大神指教having been done的用法。

Dreamout

17. 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

那个D选项老师说having been sighted时态有误。怎么有误了？能不能请大神说得详细点？

还有C选项省略也很合理啊。不就省了主句的主谓么？补上 Sunspots are就好啦。觉得这题根本问题是although 和but的逻辑关系体现，这里不是让步而是转折。

但是关于那个having been done还是希望大牛来解答一下!

医生吃鱼

1、although和but从句意角度来说都可表示转折，目前没有看到GMAT以although和but的含义区别作为选项的错误。

2、although出现在句中，该although从句中不能省略主谓。OG答案解释是这么说的，另外OG中也找不出although从句省略主谓的正确例子。

3、having been done这个结构，只能做状语修饰主句。D选项中的although从句里应该有完整的主谓，having been done这个状语位置不明。

4、having been done结构中的动作时间，是早于主句动作的时间。但是该结构一般被认为wordy，因为它可以被done替换。
我在GMAT中只碰到过一个having been done算正确的句子：
Prep07-SC-154 ：Some patients who do not respond to therapies for depression may simply have received inadequate treatment, having, for example, been prescribed a drug at a dosage too low to be effective or having been taken off a drug too soon.

5、不要太纠结having been done这个结构，只要记住它就像with独立主格结构一样，不是必错的排除标志，但很少情况下是正确的。

415lethe

having done可以做非限定性修饰，不能做限定性修饰。
夸克的语法大全里面明确写出having done做限定性修饰是错误的：
The perfective aspect cannot usually be expressed in the finite clause:
wrong: The man having won the race is my brother.
correct: The man who has won the race is my brother.

When having done 结构一定错，因为不应该有 when。单是 Having done 就够了。Have 有很多地方与正牌动词不同，When 后就不能用 having 了。原因是 having done 是过去，而 when 是当时，所以有冲突。
（同理的after/before A do sth. when B do sth.或者after/before when，这样的结构都是不好的。）

revebien

新发现的having been done：

Rather than accept the conventional wisdom that the earth was flat, Christopher Columbus
was sent by the king and queen of Spain to see if he could reach India by traveling west.
• Rather than accept the conventional wisdom that the earth was flat, Christopher Columbus
was sent by the king and queen of Spain to see if he could reach India by traveling west.
• Rather than accepting the conventional wisdom that the earth was flat, Christopher Columbus
was sent by the king and queen of Spain to see if he could reach India by sailing west.
• Instead of accepting the conventional wisdom that the earth was flat, Christopher Columbus
sailed west to see whether he could reach India, having been sent by the king and queen of
Spain.
• Rather than accept the conventional wisdom that the earth was flat, Christopher Columbus
sailed west to see whether he could reach India, having been sent by the king and queen of
Spain.
• Instead of accepting the conventional wisdom that the earth was flat, Christopher Columbus
was sent by the king and queen of Spain to sail west to see if he could reach India.


正确选项D