听下面一段材料,回答第1-3题。 1. At what temperature should we start the freezing process? A. Just below 0℃. B. Between -15℃ and -20℃. C. As low as possible. 2. How long can most foods be stored frozen? A. For up to one year. B. For half a year. C. For 24 hours. 3. What shall we learn next week? A. About canning food. B. About removing water. C. About how to unfreeze food.