at school是固定搭配,不加定冠词the,at the zoo不是固定搭配,是一般情况,所以加定冠词the,at是表示地点的介系词,后面可以跟地点,在地点名词前面,一般加定冠词the,如:at the swimming poolat the soccer matchat the table但是,有些名词表示抽象概念或固定搭配,不加定冠词the,如:at workat schoolat nurseryat table(表示“正在吃饭”).