甲基丙烯酸甲酯和丙烯酸丁酯的共聚物是常用的涂料用丙烯酸树脂。其中甲基丙烯酸甲酯被称为硬单体,而丙烯酸正丁酯则被称为()。
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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