Sunspots, vortices of gas associated with strong

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.

2 Explanations

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Are visible and have never been are not parallel....
Can you explain a more in detail the although??

Thank you :)

Mar 4, 2017 • Comment

Adam

Hi there! Actually, "are visible... but never have been..." are in parallel. They're not in the same tense, but they are parallel. A non-parallel version of this would be something like "are visible, ... and never having been ..."

With "although," we would need to restate the subject:

"appear... , although they have never been sighted..."

Please see this blog post for more about "although" clauses:

https://magoosh.com/gmat/2012/participle-phrases-on-the-gmat/

Mar 4, 2017 • Reply

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Mike McGarry, Magoosh Tutor