Answer:
C
Explanation:
she wants to get information about the behavior of registered voters, but she surveys newspaper subscribers.
we have no clue, if they are registered voters.
if they are not, then the information does not apply.
if they are a mixture, then the survey mixed apples and oranges and does not provide usable information.
only if they all are also registered voters (which we don't know), this would provide some useful information.
but even in that last case I have to say she would have gotten information only about voters reading a specific newspaper. this particular newspaper might be one with especially short or long political commentaries. for better results the demographic sample population should cover multiple newspapers, or be newspaper independent (by picking the sample from voters registration lists instead of newspaper subscription lists).