Task: Question Generation
Input (English): Passage: Vampires are finding their own undead bodies being mutated by the pollution of the host's blood, tainted with hard drugs and sexually transmitted diseases, alcohol, diabetes, anti-depressants, and cigarettes: substances that change the blood and makes it undrinkable for vampires.  The scarcity of good blood has incited an underground civil war between various groups of vampires.  A clique of 4 vampires, led by Benedict, struggle to find sustenance by seeking victims with untainted blood.  The group is being stalked by a samurai sword-wielding vampire-killing Priest, who leaves a note on the bodies of slain vampires in the form of a playing card inscribed with the words "Live Evil".  In order to survive both their race's own fierce infighting and the biological pollution found in human blood, the group desperately seeks out Max, a "blood pusher" who steals from hospital blood banks to offer the freshest and purest blood around. But they may not have time to enjoy it, because the vengeful Priest is hot on their trail.
Output (English): What type of substance is difficult to come by?