On Monday, it froze a trading account linked to Citadel Securities, a unit of the U.S. group that also owns hedge fund Citadel LLC - the first time in the crackdown that a foreign firm confirmed one of its Chinese accounts had been suspended.
Refer to the input text as context and select the correct relationship between 'Citadel LLC' and 'hedge fund' from the available options.
Options: industry, operator, director/manager, chairperson