at once

他们同时开始说话。

They all started talking ___at ___once.

学习中心真的很小，所有学生都同时说话。

The study centre is really small and all the students talk ___at ___once.

这些烧伤会造成非常严重的内部损伤，伤者必须立即去医院。

These burns cause very severe internal injuries, and the victim must go to the hospital ___at ___once.