sorry.she isn't here()1right now2.at once3in a minute4just now.都是指马上,为什么选1

这是有区别的,不能只看中文的翻译.
right now更强调的是现在.
给你举个例子,
I am leaving right now.是指离开的动作正在发生.
I will leave at once.是指马上离开,有可能说完这句话就离开.
I will leave in a minute.也是马上离开,但是要等一会.
I have left just now.这儿强调的是已经发生过的,刚刚离开.