Instructions: In this task, you are given a multiple-choice question about healthcare. Answer the question based on your information and classify your answers into '1', '2', '3', and '4'.
Input: Question: In the titration curve of a diprotic acid, the three points whose pH only depends on the dissociation constants are:
Options: <1> The starting point and the equivalence points. <2> The first point of equivalence and the two points of semi-neutralization. <3> The first semi-neutralization point and the two equivalence points. <4> The starting point, the first semi-neutralization point and the first equivalence point. <5> The starting point and the two semi-neutralization points.
Output:
2