Multi-choice problem: Continue writing the next sentence in this paragraph:

How to change a keg
Check to make sure your keg is empty.
You'll know that your keg is empty if you open the faucet of the tap and either very frothy beer comes out or none does.
Look to see if your keg has a co2 line.

Pick from:
I. Some kegs will have a co2 tank that provides pressure inside the keg to help dispense beer. The gas also helps the beer hold its natural carbonation..
II. Some kegs are already empty if they're not quite full and only water is still left, but with a 2 " co2 line usually there will be a " co2 " somewhere on the keg. Also check your keg's fill line first..
III. The co2 line is a blue line just below the bottom of the keg with co2 in it. The co2 line is a little thicker than the co2 line because as you water the keg, it moves into the co2 line..
IV. If a bucket of beer floats up in the middle of the keg, that means your keg is filled. Some liquids stick to the " co2 " line..
I.