You can't be doing two things at once.

The receptionist recognized him at once.

接待员一眼就认出他了。

I must speak to Tania at once.

我要马上跟塔尼娅讲话。

The audience at once greeted him warmly.

观众立即对他作出了热情的反应。

The boys all began to talk at once.

所有的男孩子们立即说起话来。

She says she must speak with you at once.

她说她必须立刻跟你谈谈。

The body was too badly decomposed to be identified at once.

尸体严重腐烂，难以马上辨明身份。

All at once there was someone knocking on the door.

忽然有人敲门。

All at once, Mick's serious expression softened into a grin.

米克严肃的表情一下子变成了笑脸。

I have to go, I really must, at once.

我得走了，我真的必须马上就走。

From childhood, he was evidently at once rebellious and precocious.

从儿时起，他就明显地既叛逆又早熟。

I wrote back to Meudon at once to fix up a meeting.

我马上给缪顿回信安排会面。

All the cars were jammed together at one end of the bridge.

所有车辆都挤在桥的一头.

The executioner cut off his head at one blow.

刽子手一刀就把他的头砍了.

He became very depressed and even got suicidal at one point.

他变得十分消沉,甚至一度想自杀.

They smiled uncertainly at one another.

他们犹豫地相视而笑。

At one o'clock the rain had ceased.

一点时，雨已停了。

Promptly at one, luncheon was served.

午饭一到一点钟就上桌了。

At one stage his very life was in danger.

他的生命都曾一度处于危险之中。

All the prisoners escaped at one stroke.

所有的囚犯突然全逃了.

His achievements were blotted out at one stroke.

他的功绩被一笔抹杀.