Scientists have done a lot of r_ on dinosaurs sinse long ago.It'll be a very long p_ for the victims in Sichuan to rebuild their homes.

Scientists have done a lot of r_ on dinosaurs sinse long ago.It'll be a very long p_ for the victims in Sichuan to rebuild their homes. ____ scientists have done a lot of researth on the (H1H1) flu,there are some class for further.A.As B.Once C.If D.Although Could have done would have done should have done ____ scientists have done a lot of research on A1H1N1 flu,there are still some cases for further st____ scientists have done a lot of research on A1H1N1 flu,there are still some cases for further study.A.AsB.OnceC.IfD.Although must have been done must have done have done与have be done would have done,might have done,could have done,should have done分别表示什么意思? may have done和may have done 的区别RTmay have done和might have done should have done ,shouldn't have done.could have done,couldn't have done have+done是什么时态? have sth done意思 we have done our 情态动词+have done what have u done could never have done have sth done have done是什么时态 have sth.done