否定 I can't swim
一般疑问：Can you swim?
肯定回答:Yes,I can.
否定回答：No,I can't.
can的过去式是could把 I could swim.改成否定名，一般疑问句，否定回答和肯定回答I couldn't swim否定句Could you swim? 一般疑问句Yes, I could. 肯定回答No, I couldn't.否定回答