(A) are visible as dark spots on the surface of the Sun but have never been sighted on
Correct. No error
(B) are visible as dark spots that never have been sighted on the surface of the Sun
darkspots
That modifies dark spots which changes the intended meaning. That should refer to sunspots
(C) appear on the surface of the Sun as dark spots although never sighted at
although begins a subordinate clause without a subject + correct use is sighted on not at (as if someone sighted them)
(D) appear
...
Correct. No error
(B) are visible as dark spots that never have been sighted on the surface of the Sun
darkspots
That modifies dark spots which changes the intended meaning. That should refer to sunspots
(C) appear on the surface of the Sun as dark spots although never sighted at
although begins a subordinate clause without a subject + correct use is sighted on not at (as if someone sighted them)
(D) appear
...
![FLO – Therapy at the Club – Pre-Single [iTunes Plus M4A]](http://is1-ssl.mzstatic.com/image/thumb/Music221/v4/a4/11/88/a41188ed-0f2e-e8d5-1163-d59e373cc58c/26UMGIM30046.rgb.jpg/208x208bb.webp)
