Task: Text Categorization
Input (English): 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.
Output (English): biology