Task: Question Answering
Input (English): Question: Mesna (sodium 2-mercaptoethanesulfonate) is used together with cyclophosphamide in antitumor therapy because: 
 Options:  <1> They form a ternary complex with DNA that prevents replication. <2> Mesna inactivates a toxic metabolite that results from the activation of cyclophosphamide. <3> Both are DNA alkylating agents. <4> The oxidizing properties of mesna increase the cytotoxicity of cyclophosphamide. <5> Mesna inhibits cytochrome P-450 that oxidizes and degrades cyclophosphamide.
Output (English): 2