seen是see 的过去分词.see sb.do sth.看见某人做某事.（动作结束或习惯动作）
We see her sing songs every day
see sb.doing sth.看见某人正在做某事.We see her singing songs now
seem.1）系动词seem+形容词.He seems happy
2).不及物动词 seem to do sth.或It seems that 从句
He seems to know everythng
It seems that he is happy