等于at once，表示立刻、马上的意思，例如：
1、It is a physical impossibility to be in two places at once.同时身处两地在自然法则上是不可能的。
2、The award-winning novelist often has three or four books on the go at once.那位获奖小说家经常是三四部小说同时写的。
3、It's a lot of information to absorb all at once.要一下子消化这么多资料，真是很难。
