What is the difference between primary storage, secondary storage, and off-line storage

Let me put it clear what these notions mean. Primary memory is the main memory (Hard disk, RAM) where the operating system resides. Secondary memory can be external devices like CD, floppy magnetic discs etc. secondary storage cannot be directly accessed by the CPU and is also external memory storage. Offline storage – also known as tertiary storage. This is not a very known storage, this includes jukeboxes and tape libraries.
Difference:
 - Primary memory storages are temporary; where as the secondary storage is permanent.
- Primary memory is expensive and smaller, where as secondary memory is cheaper and larger
- Primary memory storages are faster, where as secondary storages are slower.
- Primary memory storages are connected through data buses to CPU, where as the secondary storages are connect through data cables to CPU

Iwould go with either b or c, not sure which one.