硝普钠溶液必须新鲜配制，滴注时要避光，溶液只能保存4小时。
参考答案：对
写出第二次世界大战后两极对峙的军事集团的名称。
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If a computer crashes, you will lose the file you _________unless you save it regularly.
A．are working
B．work
C．will work
D．worked
