What choice would best describe the alteration made with "Half decaf"?

The term "Half decaf" specifically refers to a blend of coffee that is partially decaffeinated. This means that the coffee contains both regular coffee (which is caffeinated) and decaffeinated coffee, resulting in a drink that has reduced caffeine content compared to fully caffeinated coffee but still retains some caffeine for those who enjoy that slight stimulant effect.

This option is appropriate because it accurately represents the nature of "Half decaf," highlighting that it is not completely caffeine-free, as all decaf would be, nor is it regular coffee, which would imply a full caffeine dose. Similarly, it does not relate to the concept of being extra caffeinated, as that description goes against the notion of "Half decaf," which intentionally aims for a lower caffeine level.