The regulator further said that only Bharti Airtel in Mumbai and Tata Teleservices in Delhi met the laid-down quality of service (QoS) benchmarks for call drop rate, which as per norms should be less than 2%.
Refer to the input text as context and select the correct relationship between 'Tata Teleservices' and 'Mumbai' from the available options.
Options: developer, owner of, headquarters location, business division