烷烃在光照条件下,芳香烃在催化剂条件下,均能与X2(Cl2、Br2)发生取代反应,而烯烃与X2(Cl2、Br2)发生加成反应。
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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