From the given sentence, extract the phrase (often noun or verb) that carries the given relationship. The generated phrase should be present in the sentence.

[Q]: Given Relationship: 'declare war on', Sentence: 'When the United States declared war on Germany on April 6 , 1917 , Hemingway tried to enlist in the army .'
[A]: declared


[Q]: Given Relationship: 'be key to', Sentence: 'As present processes are thought to explain all past events , the Uniformitarianism slogan is " the present is the key to the past . "'
[A]: key


[Q]: Given Relationship: 'become', Sentence: 'In 1869 , Andrew Johnson became only the third President who did not join the President-elect in the procession to the Capitol , nor did he attend the swearing-in ceremony .'
[A]:
became