Given the task definition and input, reply with output. 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.

Question: In the absence of oxygen, the mitochondrial citric acid cycle is inhibited because:
Options: <0> Increases the concentration of ADP, an inhibitor of isocitrate dehydrogenase. <1> The phosphorylations at the substrate level can not be produced. <2> No pyruvate available. <3> ATP synthase is inhibited. <4> The necessary coenzymes can not be reoxidized.
biology