In the context of the input sentence, determine the relationship between 'Sirtex' and 'Sydney'.
Options: distributed by, parent organization, headquarters location, distribution format

Broker Watch: Iluka Resources, Saracen Minerals, Northern Star, Corporate Travel Broker Watch: Navitas, OrotonGroup, Elysium Resources, insurance Broker Watch: Evolution Mining, Steadfast Group, Sims Metal, Energy Developments Broker Watch: Austbrokers, Fortescue Metals Group, Carnavale Resources, Valence Industries Broker Watch: Macquarie Group, BHP Billiton, South32, resources sector Broker Watch: Western Areas, Oil Search, Telstra, Evolution Mining Broker Watch: Saracen Minerals, Austal, Sonic Healthcare, Arrium Broker Watch: Decmil, Paladin Energy, Regis Resources, Universal Coal Broker Watch: Macquarie Group, Beadell Resources, Ramelius, Whitehaven Coal Broker Watch: Primary Health Care, Challenger, Mount Gibson Iron, Perpetual Broker Watch: BHP Billiton, Sedgman, Newcrest Mining, APA Group Broker Watch: Rio Tinto, Horizon Oil, Greencross, SEEK Broker Watch: CSR, Aristocrat Leisure, Northern Star Broker Watch: Iron ore majors, Aurelia Metals, Alcoa, Gryphon Minerals Broker Watch: Gold stocks, insurance sector, Incitec Pivot Broker Watch: Crown Resorts, Aurelia Metals, Orica, Amcor Broker Watch: Asciano, BlueScope Steel, James Hardie, Cue Energy Broker Watch: Energy sector picks, REA, PacBrands, Treasury Wine Broker Watch: James Hardie, Brambles, Recall Holdings, GPT Group Broker Watch: Air New Zealand, Scentre, Aurizon, Transurban Group Broker Watch: Wesfarmers, Myer, Sandfire Resources, Sydney Airport Broker Watch: Brambles, Arrium, Tabcorp, Monadelphous Group Broker Watch: Origin Energy, Flight Centre, iSelect, Dexus Property Group Broker Watch: Fletcher Building, IAG, BT Investment Management, CSR Broker Watch: Woolworths, CSL Ltd, Metcash, Scentre Group Broker Watch: Sydney Airport, Resmed, Challenger Financial, Arrium Broker Watch: TFS Corporation, Western Areas, NAB, Spark Infrastructure Group Broker Watch: Primary Health Care, Metcash, Ten Network, Sonic Healthcare Broker Watch: Cover-More, SCA Property Group, Telstra, Boral Broker Watch: Federation Centres, Rio Tinto, CBA, Alexium International Broker Watch: Goodman Group, QBE, Adelaide Brighton, Seven Group Holdings Broker Watch: Eclipx, Independence, Alumina, ANZ Banking Broker Watch: ERA, Mirvac, Qube, DUET Broker Watch: QBE, Goodman, Seven, TPG Broker Watch: Greencross, Qantas, South32, Woolworths Broker Watch: Mesoblast, APA Group, Recall, Iluka Broker Watch: AGL, AWE, Qube, Nine Broker Watch: Metcash, Fleetwood, Otto Energy, McPherson's Broker Watch: BHP, Newcrest, Yowie, REA Broker Watch: Virtus Health, CSL, Spotless, Crown Broker Watch: Slater & Gordon, UGL, Flight Centre, Sirtex Broker Watch: Ardent, BWP Trust, Domino's, DUET Broker Watch: AGL, ALS, Ramsay, DuluxGroup Broker Watch: Woodside, Adelaide Brighton, Programmed, Brambles Broker Watch: BHP Billiton, WorleyParsons, Telstra, St Barbara Broker Watch: Ramsay Health Care, WOW, Dulux, Spark ​
headquarters location