Definition: In this task, you are given a multiple-choice question about healthcare. Answer the question based on your information and classify your answers into '1', '2', '3', and '4'.
Input: Question: What is the purpose of the phthalyl group in phthalisulfatiazole ?: 
 Options:  <1> Improve intestinal absorption. <2> Prevent intestinal absorption. <3> Improve the passage through the blood-brain barrier. <4> Prevent passage through the blood-brain barrier. <5> Increase the affinity towards the therapeutic target of the drug.
