Correct Response: C. A more upvoted answer implies the response has the confidence of the forum community. If the community is reliable, the answer is likely to be as well. A is incorrect because the amount of time a writer has spent in this particular forum does not indicate their level of expertise relative to the student's question. B is incorrect because profile biographies may or may not be accurate, depending on the forum’s identity verification policies. D is incorrect because the length of a response is unrelated to its validity.