Correct answer:
B.) la visa
Visa translates into the same English word visa and is an authorized document or mark you can get in your passport to enter or leave a country. So you need tourist visa (visa de turista) if you want to enter the U.S. In this way, we can write this sentence as hay que solicitar visa de turista para poder entrar a los Estados Unidos that translates into you must apply for a tourist visa to enter the United States