Which is a perceived threat to the credibility of digital publications
a. easy availability or e-publishing platforms
b. easy usability of e-published materials
c. enhanced audio and visual elements in digital publications
d. possibility of converting out of point books into digital publications

A. easy availability or e-publishing platforms

Explanation:

Everyone these days can publish on various platforms, from social medias to blogs and numerous other ways. While it's great to have a bigger variety of sources of information, it's also getting harder and harder to identify the real provider of the information and its source.

Before, you had reputable content distributors (like newspapers), with professionally formed journalists to verify the information before publishing it.  Yes, the information took longer time to get to the population, but it was verified.  These days, everything can appear live on the medias, and sometimes it's hard to distinguish what is real from what is fake.