用干冰作致冷剂保存食品有哪些优点?
参考答案:
干冰升华会吸收大量的热,使环境温度降低,升华后无残留物,不会弄湿和污染食品,且产生二氧化碳能抑制细菌的繁殖.
You______ her in her office last Friday; she's been out of town for two weeks.
A.needn't have seen
B.must have seen
C.might have seen
D.can't have seen
1615, 2422, 3629, 5436, ()
A.8150
B.8143
C.7850
D.7843