This is a test of commonsense with single/multi-choices. Complete the next sentence:

How to keep the nose moist to prevent nosebleeds
Use a humidifier.
You can use either a cool water humidifier or a vaporizer. When the air is very dry, any increase in humidity will help prevent a nosebleed.

Select from the following. I. Humidifiers tend to dehumidify more easily than a vaporizer, because they have low drying cycles. If you want the environment to become more dry, consider using a mist humidifier.; II. A combination humidifier is ideal for cold weather. Dry air can often interrupt the healing process and cause nosebleeds.; III. Moistening the air at night will also make it easier to breathe and to sleep. If you don't have a commercial humidifier, you can make one by putting a pot of water on the radiator/heating in the winter.; IV. Put the humidifier on for half an hour or two a day until the nosebleed subsides. Make sure that the humidifier is not connected to any heat sources.;
The answer is:
III.