What is a key difference between reservation buying and auction buying?

Reservation buying means pre-packaged lineups, while auction buying is for individual impressions.
Reservation buying includes hard-to-sell inventory, while auction buying does not.
Reservation buying is done manually, while auction buying is done through a Google representative.
Reservation buying is done programmatically, while auction buying is done manually.

The correct answer is:

Reservation buying means pre-packaged lineups, while auction buying is for individual impressions.