书上有一句I am playing basketball at school 我想问的是 为什么school 前面没有冠词

书上有一句I am playing basketball at school 我想问的是 为什么school 前面没有冠词 I'am playing for I'am playing for I am（）.playing football playing the football play football I am playing football （对 playing football 提问） i am always playing 和 i always am playing那个对 I am no playing computer .改病句可不可以 I am playing computer . i am getting some soy sauce,i am doing push-ups,i am playing hidden i am playing tennis and singing.和i am singing as i playing tennis.谁更好?有语法错误吗? I am practicing playing the violin.有语病吗? I am playing the violin.改成一般疑问句 I am playing the violin.改成一般疑问句? I am playing the violin改成一般疑问句 英语翻译I am not interested in playing games _ _ . I am playing computer games now.(改为一般疑问句) I am interesting in playing basketball是对是错... I am playing chess?(变成一般疑问句） i am playing basketball now.改一般疑问句 再问一个：I am playing basketball 改成复数形式