[求助]大全677

1.        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（C）

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

are visible or appear,彻底晕了，那位能给讲讲，先谢了！

A. 被动语态 are visble as;    be sighted ON the poles or equator

C. 主动语态 appear as ;       be sighted AT the poles or equator,     AT is better.

我觉得 visible 在这里句意也有问题， 从常理上讲sunspots are not visible.

不知道对吗？请指点一下

sunspots are visible 没错的，太阳黑子

但是 sunspots are visible as 就有问题了，表达得很别扭。

请教关于although

1项中although前面用逗号隔开,是否后面要加上主语?

2:although可以这样省略?

我看到有NN说这里BEEN可以省略,但我记得如果主句没有出现BE动词的谓语形式,后面好象省略有问题吧?

请赐教