A local television news station includes a viewer survey question about a current issue at the beginning of every evening news broadcast. Viewers are invited to use social media to respond to the question. The results of the survey are shared with the audience at the end of each broadcast. In relation to the opinions of the population of the region, which of the following is a possible reason why the results of such surveys could be biased?

I. Viewers with strong opinions about the current issue are more likely to respond than are viewers without strong opinions.
II. The opinions of viewers of one television station are not necessarily representative of the population of a region.
III. Viewers with access to social media are not necessarily representative of the population of a region.