Task: Text Categorization
Input (English): Question: The term isocratic is used in high pressure liquid chromatography (HPLC) when: 
 Options:  <0> The mobile phase is at a constant temperature. <1> The stationary phase is in equilibrium with the mobile phase. <2> The mobile phase consists of a single solvent with a constant composition. <3> The flow rate of the mobile phase is regulated. <4> All the options are correct.
Output (English): chemistry