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: Could a glass electrode be used as a reference electrode ?:
Options: <1> Yes, if the glass electrode is a combined electrode. <2> Yes, if a mercury electrode is used as the indicator electrode. <3> No, since the glass electrode is a selective electrode. <4> No, because its foundation is not Nerstian. <5> Yes, if the determination is made in a buffered medium.
Output:
5