[单项选择]Questions 47 to 56 are based on the following passage. Before refrigerators, homes usually had ice boxes. But (47) way to keep food cool without the need for electricity is to use an evaporative cooler. This is easy to make and does not even use (48) . A. Cold (54) in a freezer, however, can keep foods in good condition fox months after the (55) season. Yet foods can be damaged if they are kept too cold The British development group Practical Action says the best way to prepare foods for storage is at (56) time while still in the field. Use a sharp knife to avoid damage.