单选题 Centuries ago, men discovered that (1) moisture from food helps to (2) it, and that the easiest way to do this is to expose the food (3) sun and wind.
Nowadays most foods are dried (4) . The conventional method of such dehydration is to put food in chambers (5) hot air is blown at temperatures of about 110℃ at entry to about 43℃ at (6) . This is the usual method for drying (7) as vegetables, minced meat, and fish.
Liquids such as milk, coffee, tea, soups, and eggs may be dried by pouring them over a (8) horizontal steel cylinder or (9) them into a chamber through which a current of hot air (10) In the first case, the dried material is scraped off the miler as a thin film which is then (11) small, though still relative coarse flakes. In the second process it falls to the bottom of the chamber as a (12) powder.
Dried foods (13) less room and weigh (14) the same food packed in cans. They do not need (15) in special conditions. For these reasons they are (16) climbers, explorers, who have little (17) . They are also (18) housewives because it takes so little time to cook them. Usually it is just a case of (19) the dried out moisture with (20) water.