A. If no $storeManager is provided, Magento's code generator creates a shell concrete class based on \Magento\Store\Model\StoreManagerInterface

B. Magento finds all classes that implement \Magento\Store\Model\StoreManagerInterface (ordered alphabetically) and injects the first class.

C. Magento looks to the di.xml files in the entire system for a preference node for \Magento\Store\Model\StoreManagerInterface. This class is constructed and injected

D. Magento throws an exception because you cannot instantiate an interface