in no time,right away, right now, at once 有何差别,细讲

right now指at this moment, right away指毫不犹豫或毫不耽误的“立即”。
in no time 没有否定之意,它表示:立即.一般放在句末.
at once 立刻，马上；同时，一起

at once,in no time,right now,right away
这四个短语常可互换,只是说话角度上有细微区别.
1.at once等于now,without delay.如：
Do it at once.立刻就做.Come here at once!马上就来!
at once 也有“at the same time,together”的意思.如：
Don’t all speak at once!不要全体同时说话!
注意：all at once=suddenly
2)in no time
very quickly；very soon很快地；不久
With a pair of scissors,she can turn out a beautiful design in no time．用一把剪刀,她可以立即剪出一个美丽的花样来.
Take this medicine,and it will cure you in no time．吃了这种药,你的病马上就会好的.
They finished the work in no time at all．他们立刻完成了这项工作.
3.right now指at this moment,right away指毫不犹豫或毫不耽误的“立即”.如：
If you get the address,let me know right away.你看到地址,请立即告诉我.
Shall we begin right now?我们现在就开始吗?
(4)
at once 1.立刻,马上;同时；是一个副词短语