Hi anceer,
Let's first identify/ understand the Economist and Journalist's arguments.
The Economist is arguing that Professional Software Designers have more creative ideas and therefore can produce more useful software than the volunteers that produce open source product.
The Journalist responds with saying that although she was initially skeptical, she would have been unable to write her article without the interviews from these volunteers.
The best way to attack this problem is to eliminate answer choices.
(A) Changing an opinion for valid reasons doesn't render it invalid. This doesn't show a flaw.
(B) The passage makes no mention of the Journalist refusing to interview professional sw designers. This doesn't show a flaw.
(C) This addresses the issue. The Journalist fails to address the Economist's main argument about the creativity disparity between professionals and volunteers.
(D) We know nothing about the Journalist's writing history. This doesn't show a flaw.
(E) The Economist is not arguing about popularity. This doesn't show a flaw.
Hope this helps! Good luck studying!
-Lighthouse Prep