过去时动词He could't help laughing when he heard the result.这里为什么help不用过去时?

过去时动词He could't help laughing when he heard the result.这里为什么help不用过去时? could't help doing sth 和can't help doing sth 在时态上有区别吗也即是could't help doing sth.可以用在现在时吗?can't help doing sth 可以用在过去时吗? could后面的动词还要用过去时吗 he could't help to sing when he knew he had passed the exam The doctor said he could do nothing to help him.动词不定时做什么句子成分 He said he couldn't follow me.句中couldn't能换成can't吗?He said he couldn't follow me.他说他跟不上我表示过去的能力时只能用can的过去式could吗?我查了资料又说了许多表示过去能力不用could的情况,感觉好 he need't any help ,中的needn't为情态动词 help是名词,为什么这句话还对. Wish将来时态虚拟语气～这是wish的虚拟结构：主句 　　从句 　　现在时 　　过去时 　　过去时 　　过去完成时 　　将来时 　　would/could +动词原形 有几个例子：1.I wish I were as tall as you.2.He I don,t think he could have done such a stupid thing last night______?did he ,could have done表示对过去情况的推测,且有明显的时间状语 last night,故用过去时.这样理解对吗,还有 能用 could he 么, But before l could help him,he told me he wouldn't need an ambulance any longer.中文意思? He could have come to help us ,but_____.a.he didn't b.he hasn't c.he hadn't d.he can't为什么选a不选b如果后面写反义疑问句是不是用didn't he? 情态动词不是没有时态的变化吗?为什么can 的过去时是could? He couldn't understand spoke English before he moved to Canada.为什么speak和move用过去时?一句话中不是只有谓语动词表现时态就可以了么?为什么speak和move都要用过去时? 英语中的am is are用法和情态动词是什么?不要百度一下粘过来.在这下面哪个是情态动词?He could be here soon.他很快就来.We can't carry the heavy box.我们搬不动那箱子.I'm sorry I can't help you.对不起,我帮 情态动词的过去式后面能接完成时吗?比如can he have told a tie和could he have told a tie?这两句话有什么区别?是could引导的句子比can的更委婉一些吗?除此之外could还能用于现在和过去的虚拟语气？ The boy can't ride his bike.He wants to know who （break）it动词填空 用现在完成时还是过去时? 句子could you asked sb.to do sth.中为什么could 后面ask是过去时,could后面动词不是原型么?同上 I don't think he could have done such a stupid thing last night,__ A.could he B had he Cdid he这里could不是情态动词,have不是助动词吗?为什么要用did?（答案选C）