I am queen.为什么不用加a?

I am queen.为什么不用加a? i agree为什么不用在I后面加AM I am Chinese.中Chinese前用不用加a? I am a king ,and you are my queen I am queen ,Not princess I am Chinese.为什么Chines前不用冠词a? I am a Chinese girl.为什么不用:I am an Chinese girl. 为什么要说If I were a fairy,而不用If I am a fairy? I am not Chinese boy I am not a Chinese 为什么后者要加a那 I am busy yesterday为什么加am I am French.中French前为什么不加a? I am worker 为什么要在worker前加a?