Sentence Correction

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

I would chance it and go for A. Others just all seem to have a flaw in them:
B: reverses meaning (NOT on surface) and has a dodgy word order ('never have been')
C: 'although never sighted' - sounds like a fragment - what is the subject? Should be 'although they were never sighted...'
D: same problem, no subject after 'although'
E: restrictive clause after 'which' refers to 'surface' instead of 'sunspots'.