In this task, you're given an open-domain question. Your task is to provide an answer to the given question. There is only one unique answer for each question. Your answer should be short, and refer to an entity, date, number, etc. Do not put your answer in the context of a sentence.

Ex Input:
Where does the ulna articulate with the humerus?

Ex Output:
semilunar notch


Ex Input:
Why did the united states pursue a policy of containment?

Ex Output:
prevent the spread of communism after the end of World War II


Ex Input:
What are the names of the twin towers?

Ex Output:

1 World Trade Center and  2 World Trade Center