臭氧龟裂
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
橡胶在阳光、热、空气(氧气和臭氧)或机械力的反复作用下,表面会出现变色、变硬、龟裂、发黏,同时机械强度降低,这种现象称为( )
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