Jack is English.He is an English boy.为什么第一个English不用冠词?

Jack is English.He is an English boy.为什么第一个English不用冠词? Jack is an English boy. Jack is an English boy. He is a good student. He is twelve y 合并句子he is an English boy.Jim is an English boy,too.he is an Is he an English boy.复数形式 He is an English hello,my name_____Jim.He is an English boy.his _____is Jack Mike is an English boy. He is an English boy 同义句 改为 The boy ( ) ( ). Jim is ( ) English.He is ( ) English boy.A.an;an B./;an C./; He'is( )English.为什么不用加冠词?另外意思是啥? I guess______name is peter,he is an English boy .