Task: Text Categorization
Input (English): Question: A selective calcium electrode is characterized by having: 
 Options:  <0> A membrane that is a solid crystal. <1> An internal solution of 0.1 M HCl <2> An internal silver electrode. <3> A membrane of silver salts. <4> An internal aqueous solution of CaCl 2 saturated with AgCl.
Output (English): chemistry