What is the relationship between 'Equinix' and 'data center' in the context of the input sentence.
Options: currency, position held, subsidiary, product/material produced

-- U.S. data center operator Equinix (NasdaqGS: EQIX - news ) to acquire British peer Telecity Group (LSE: TCY.L - news ) (notified Sept. 24/deadline Oct (HKSE: 3366-OL.HK - news ) .
product/material produced