食品的冷藏只能减缓食品变质及产生危害的程度
参考答案:对
I had been puzzled over the problem for over an hour without any result, ____ all at once the solution flashed across my mind.
A.while
B.when
C.then
D.as
宽带无线接入技术主要有本地多点分配业务(LMDS)和【 】两种。