at once
1．very soon； immediately立刻
The telegram must be sent at once．电报必须立即发出。
I recognized him at once．我立刻就认出了他。
2．both； equally同样；兼
He is at once a statesman and a writer．他既是一位政治家，也是一位作家。
He was at once happy and sad．他悲喜交集。
The book is at once interesting and instructive．这本书既有趣又有教育意义。