Choice D is the best answer. Although the passage initially states that traditional news authorities were once implicitly "trusted"(line 29,"regarded...authoritative") regarding the content they produced, it goes on to note that "as part of the general process of the transformation of authority . . . the demand has been for all authority to make explicit the frames of value which determine their decisions" (lines 33-38,"As...decisions"). The modern audience, in other words, wants to hear not only the stories a news organization produces but also the values that form the foundation of that organization's beliefs.
Choices A, B, and C are incorrect because lines 33-38("As...decisions") make clear that the expectation traditional authorities now face is the need to "make explicit the frames of value which determine their decisions," not that they shouldn't be affected by commercial interests (choice A), that they should work for the common good (choice B), or that they should consider the context of public versus private knowledge (choice C).