In this task, you are given a question and answer options for that question. Using this information, you have to classify each text into different topics: medicine, nursery, psychology, chemistry, pharmacology, biology.
Q: Question: The forces that stabilize the alpha helix are:
Options: <0> Intra-chain hydrogen bridges parallel to the axis of the helix. <1> Disulfide bridges between methionines. <2> Hydrogen bridges between chains perpendicular to the axis of the helix. <3> Van der Waals forces among the radicals. <4> Links between lysine radicals.
A:
biology