Answer: I would contend that the right answer is the D) The overwhelming number of geese at the park has become unacceptable.
Explanation: Just to elaborate a little on the answer, it can be added that the viewpoint is the author's point of view. The previous sentences do not contain a point of view, but a series of past events: the author and his or her family attended a picnic at the park and they were mobbed by geese that stole their lunches. In addition, the introductory sentence exposes the reason why he or she is writing the letter. It is only at the end when he or she provides a personal opinion about the presence of geese at the park—"it has become unacceptable," he or she declares.