다음 글의 주제로 가장 적절한 것은?


In addition to controlling temperatures when handling
fresh produce, control of the atmosphere is important.
Some moisture is needed in the air to prevent
dehydration during storage, but too much moisture can
encourage growth of molds. Some commercial storage
units have controlled atmospheres, with the levels of
both carbon dioxide and moisture being regulated
carefully. Sometimes other gases, such as ethylene gas,
may be introduced at controlled levels to help achieve
optimal quality of bananas and other fresh produce.
Related to the control of gases and moisture is the
need for some circulation of air among the stored
foods.


① The necessity of controlling harmful gases in atmosphere
② The best way to control levels of moisture in growing
plants and fruits
③ The seriousness of increasing carbon footprints every
year around the world
④ The importance of controlling certain levels of gases
and moisture in storing foods