Definition: In this task, you're given a statement and three sentences as choices. Your job is to determine the neutral choice based on your inference from the statement and your commonsense knowledge. The neutral choice is a sentence that neither agrees nor disagrees with the statement. Indicate your answer as '1', '2', or '3', corresponding to the choice number of the selected sentence. If sentence X agrees with sentence Y, one's correctness follows from the other one. If sentence X disagrees with sentence Y, they can not be correct at the same time.
Input: Statement: Four are essential to case study  iteration, OTTR, triangulation, and ruling out rival explanations. Choices: 1. Four are needed for making sure the rival explanations are in fact correct. 2. Four are needed for making sure the rival explanations are ruled out. 3. Four are needed to prove that the rival explanations can't happen because of gravity.

3