I want to know the answer to the following question:
To ensure a minimum density of signal transitions  remains in the bitsream, what does USB use?
All the background I'm provided with is that "USB encodes data using the NRZI line coding; a 0 bit is transmitted by toggling the data lines from J to K or vice versa, while a 1 bit is transmitted by leaving the data lines as-is.". Is that enough to answer the question?