冷冻干燥剂由哪些系统组成?
参考答案:
冷冻干燥机由冻干箱、冷凝器、冷冻系统、真空系统、冷热交换系统组成。
Nothing that he suggested ____ to be of any use. [ ]
A. prove
B. proved
C. proving
D. to prove
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