All at once there was someone knocking on the door.
忽然有人敲门。
She wanted to laugh and weep all at once
她哭笑不得。
I feel terribly sleepy all at once
我突然觉得特别困。
In the hot sun the rain-washed herbs smelled sharp and spicy and sweet all at once.
烈日下，被雨水冲刷过的香草闻起来既冲又香气扑鼻。
All at once I fell into a state of profound melancholy.
我立即陷入无限的愁思之中。