Task: Question Answering
Input (English): 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 (English): 2