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.

Sentence: 'Shenzhen was the mainland Chinese rival to Hong Kong before Hong Kong became part of China , but has only recently decided to move toward economic cooperation , instead of competition , with the special administrative region .', Argument/Subject 1: 'hong kong', Argument/Subject 2: 'china'
be part of