Task: Question Answering
Input (English): Question: Why does carbenicillin have a low antibacterial activity by mouth ?: 
 Options:  <1> It is degraded by beta-lactamases in the digestive system. <2> He undergoes first-pass hepatic oxidative metabolism. <3> It binds covalently to plasma proteins. <4> It is decarboxylated in the acid medium of the stomach giving rise to benzylpenicillin, which is also unstable in that medium. <5> It is highly lipophilic, which is why it is not released correctly from oral administration forms.
Output (English): 4