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 - long,wordy.
(B) are visible as dark spots that never have been sighted on the surface of the Sun - that never have been - wrong use.
(C) appear on the surface of the Sun as dark spots although never sighted at - Short,concise,although conjugates a sentence with verb and subject. IMO
(D) appear as dark spots on the surface of the Sun, although never having been sighted at - wrong use never having been sighted.
(E) appear as dark spots on the Sun’s surface, which have never been sighted on - which antecedent is unclear.
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A) looks fine
B) (SUN is written twice? <- maybe a typing error). Disregarding this, "that" is a "necessary" modifier. I do not think it should be used.
C) unclear whether Sun or dark spots is/are "never sighted"
D) the same as C
E) although "have" clearly refers to "dark spots", "which" should be in touch to "dark spots", not "Sun".

OG question OA A..please explain in detail!
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I have chosen A for this question:

A. The two verbs are parallel here. "Are visible" tells us that this fact is true in the current time and is parallel to "have never been sighted" that suggests we have still not been able to see these sunspots on the poles or equator of the sun. Although the tenses are different, it is still parallel because of the meaning of the sentence. The use of "are" gives us correct subject verb agreement.

B. The last part of this answer choice makes no sense. "Sighed on the surface of the sun then sun's..." is definitely not correct.

C. I had 2 issues with this answer choice. Firstly, the simple past tense of the verb "sighted" suggests that this fact occurred in the past and is not valid in the current time frame, so we are left wondering if this is true or not in the present time. I believe the intention of the sentence is that we have not been able to see these sunspots on the poles or equators in the past and that fact continues today. Therefore, simple past tense usage is incorrect. Also, I was confused by the use of the word "although" because it starts off a subordinate clause, but this clause does not have a subject.

D. The subordinate clause set off by the word although does not have a subject.

E. Which seems to modify sun's surface.

I think the correct answer is A. The question basically compares Sunspots and dark spots on the surface of the Sun. The choice A rightly compares these two and it is more precise compared to B . Moreover B has "that" which is unnecessary. So go with A.
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