Right answer is A even though 1000Sc says is C.
This is a OG 11th edition question. (pg. 666 , question #9)
The OA is A from the OG11
below are their explainations
A) Correct. This sentence clearly and correctly draws a contrast between where sunspots are found and where they are not.
B) changing the modifying clause so that that never ... sun distorts the meaning of the sentence; the contrast is lost.
C) Although typically introduces a subordinate clause, which has a subject and a verb, but here there is no subject and sighted is not a complete verb
D) Although typically introduces a subordinate clause, which has a subject and a verb, but here there is no subject of the clause and having been sighted is not a complete verb phrase.
E) The relative pronoun which should immediately follow its referent; here which illogically follows surface and its intended referent, either sunspot or dark spots, becomes unclear.