Answer the following question: What is the last name of the person who volunteers because he is interested in Betsy?  Answer the above question based on the context below:  Travis Bickle, a 26-year-old honorably discharged U.S. Marine, is a lonely, depressed young man living in isolation in New York City. He takes a job as a taxi driver to cope with his chronic insomnia, driving passengers every night around the city's boroughs. He also frequents the porn theaters on 42nd Street and keeps a diary in which he consciously attempts to include aphorisms, such as "You're only as healthy as you feel." Travis becomes infatuated with Betsy, a campaign volunteer for Senator and presidential candidate Charles Palantine. After watching her interact with fellow worker Tom through her window, Travis enters to volunteer, as a pretext to talk to her, and takes her out for coffee. On a later date, he naively takes her to see a pornographic film, which offends her, and she goes home alone. His attempts at reconciliation by sending flowers are rebuffed, so he berates her at the campaign office, before being kicked out by Tom. Travis is disgusted by the sleaze, dysfunction, and prostitution that he witnesses throughout the city. His worldview is furthered when an adolescent prostitute and runaway, Iris, enters his taxi, attempting to escape her pimp, Sport. Sport drags Iris from the taxi and throws Travis a crumpled $20 bill, which continually reminds Travis of her and the corruption that surrounds him. A similarly influential event occurs when an unhinged passenger gloats to Travis of his intentions to murder his wife and her lover. Travis confides in fellow taxi driver Wizard about his thoughts, which are beginning to turn violent; however, Wizard assures him that he will be fine, leaving Travis to his own destructive path.
Answer:
Bickle