Instructions: In this task, you are given a question and a context passage. You have to answer the question based on the given passage.
Input: Where else was ebola a threat?, Context: Nigeria was the only country in Africa to have never eradicated polio, which it periodically exported to other African countries; Polio was cut 98% between 2009 and 2010. However, a major breakthrough came in December 2014, when it was reported that Nigeria hadn't recorded a polio case in 6 months, and on its way to be declared Polio free.  In 2012, a new bone marrow donor program was launched by the University of Nigeria to help people with leukaemia, lymphoma, or sickle cell disease to find a compatible donor for a life-saving bone marrow transplant, which cures them of their conditions. Nigeria became the second African country to have successfully carried out this surgery. In the 2014 ebola outbreak, Nigeria was the first country to effectively contain and eliminate the Ebola threat that was ravaging three other countries in the West African region, the Nigerian unique method of contact tracing employed by Nigeria became an effective method later used by countries, such as the united States, when ebola threats were discovered.
Output:
united States