sunspots

[j_shreyans]

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


OAA

Why visible, why not appear?

why have been is required ?

Please suggest me...

[GMATGuruNY]

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

In C and D, sighted AT the Sun's poles implies that no one located AT the Sun's poles has ever seen sunspots -- not the intended meaning.
The intended meaning is that sunspots have never been sighted ON the Sun's poles.
Eliminate C and D.

In B, dark spots that never have been sighted on the surface of the Sun changes the meaning.
The intended meaning is that SUNSPOTS (not dark spots) have never been sighted on THE SUN'S POLE OR EQUATOR (not the surface of the sun).
Eliminate B.

In E, which have (plural) seems to refer to dark spots -- the nearest plural antecedent -- implying that dark spots have never been sighted on the Sun's poles or equator.
The intended meaning is that SUNSPOTS have never been sighted on the Sun's poles or equator.
Eliminate E.

The correct answer is A.

Why visible, why not appear?

It is fine to say that sunspots appear.
C, D and E are incorrect for other reasons.

why have been is required ?

A: Sunspots have never been sighted on the Sun's poles
Here, have never been sighted implies that -- SO FAR -- we have not seen sunspots on the Sun's poles but that someday we MIGHT see them there.