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'.

Question: The immersion oil used for microscopic observation:
Options: <1> Protects the sample from the oxidizing effect of air. <2> Lubricate the objective lens. <3> Reduces refraction and increases resolution. <4> It acts as a lens that increases magnification. <5> Avoid dehydration of the preparation.
3