In January this year, Transstroy signed three car loan agreements for Rs 4.73 crore with Alphera Financial Services, a financing arm of BMW Group Financial Services, to buy a Lamborghini Huracan coupe, a Mercedes Benz S350 and a BMW Z4 sDrive.
Analyze the relationship between 'BMW Z4' and 'BMW' within the context of the input sentence.
Options: brand, location of formation, parent organization, original broadcaster