Q1: Sunspots, vortices of gas associated with strong eleconmagnetic 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 the

(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

which one is the correct anwser and why?

thanks

我看A最顺眼

同一楼上的，只有A的逻辑表达最合理

选c首先用at poles and equator,不用on

此外done 优于having been done

“C 的sighted 前面少了系动词, Although 后面要跟完整的句子”

这个不是关键，而且是语法许可的。