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.

他试图同时回答所有问题，但这让人不知所措。

He tried to answer all the questions ___at ___once, but it was overwhelming.