Respuesta :
A) would be the best answer.
Since there are two different thoughts in this sentence, a comma is needed.
But it would not make sense for there to be a "for" directly after the comma, for this is not a cause-and-effect sentence.
So, by process of elimination, we find that A is the correct answer.
I believe the answer you are looking for is A. Thomas Edison was an inventor, but Alexander Calder was an artist. :)