GMAT Sentence Correction (SC) | Re: Sunspots, vortices of gas associated with strong

This is indeed not a test of //ism; rather it is about meaning and grammar. If you are thinking about the verb //ism here, there is only one // marker, namely, the fanboy conjunction but. The verbs on either sides of the ‘but’ are in present and present perfect tenses, which is acceptable.

(A) are visible as dark spots on the surface of the Sun but have never been sighted on ---- correct choice.
(B) are visible as dark spots that never have been sighted on the surface of the Sun -----