二、词汇语法题(每空1分,共20分)
Directions: There are 20 incomplete sentences in this section. For each sentence there are four choices marked A, B, C and D. choose one answer that best completes the sentence.
It is easy to ( )one state of matter from another.
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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