From the information given, only B and C can be eliminated. The other two all start by going down. If a was plus you would get a graph looking like B. The midline and period should not be confused. All of them have a midline of y = 0. So that doesn't help very much. You actually can eliminate C because that is not one full cycle. But there is no way to choose between A and D without knowing about the period. If you modify the question in your comments section, I'll explain the difference between A and D. Add a comment either in this answer or your question, please.