Pls Help me explain

Please post the complete question, OA, and source when posting questions.

Here is the complete question from OG2015 #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

First, we want to understand the meaning of the sentence. We're discussing two important points about sunspots: a) they're visible as dark spots, and b) they've never been seen at the poles or equator.

You are correct that "sunspots" is the subject in every answer choice. We can say "sunspots are visible as dark spots" or "sunspots appear as dark spots" - either would be correct. With "appear," though, we lose a little bit of the contrast between "they're visible generally... but we haven't seen them in certain places."

The main issue with both C and D is that "although" should set up a subordinate clause. We need both a subject and a verb after it, such as "although they have never been sighted." "Although never sighted" and "although never having been sighted" are incomplete ideas.

In C (what you list as A above), "sighted" is indeed passive voice - but that's not a problem! Passive voice is not inherently wrong. In fact, every answer choice is passive, because we're talking about what can be SEEN on the sun (the implication is that it's seen by humans, but we don't need to spell that out).

Here's a complete breakdown of the answer choices:

(A) are visible as dark spots on the surface of the Sun but have never been sighted on
Correct!

(B) are visible as dark spots that never have been sighted on the surface of the Sun
The modifier "that" is incorrectly applied. It's illogical to say that sunspots are visible as dark spots THAT have never been sighted.

(C) appear on the surface of the Sun as dark spots although never sighted at
"Although never sighted" is incomplete - there should be a subject and a verb there.

(D) appear as dark spots on the surface of the Sun, although never having been sighted at
Same issue as C.

(E) appear as dark spots on the Sun's surface, which have never been sighted on
The "which" is misplaced here. They appear as dark spots which have never been sighted? Illogical.

The answer is A.

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