是he had sit down还是sat?为什么

是he had sit down还是sat?为什么 sit的过去式是sat还是sit She sat down这里的down是副词 那谓语是sit还是sit down吖 She came in 这里的谓语是 please,sit down中的down是介词还是副词?为什么会出现sit down on one of these she saw that they had sat down中的that是连词还是从句的什么词? Hardly had I sat down when he stepped in I had hardly sat down when he stepped in He sat down and had a test.sat本身就已经是动词了,down也是,两个动词怎么可能在一起? he sat down on the ________ (sit) nearest to the door. 是sit down at the table还是sit down beside the table he wanted to find a seat to sit down还是sit on? Sit down,please的回答是OK还是Thank you