Instructions: Given a sentence and two mentions from the text (arguments), indicate a phrase (a verb or noun phrase) that describes the relationship between the provided arguments.
Input: Sentence: 'Flock is built on top of Firefox and the team have been working hard over the last couple months to upgrade Flock to the new Firefox 3 base .', Argument/Subject 1: 'flock', Argument/Subject 2: 'firefox'
Output:
be build on