at once 是什么時態

　　A computer can perform many tasks at once.

　　電腦能同時做多項工作。

　　She fell in with my idea at once.

　　她立刻同意了我的主意。

　　We have several projects all on the boil at once.

　　我們熱火朝天地同時上馬了幾個項目。

　　It is a physical impossibility to be in two places at once.

　　同時身處兩地在自然法則上是不可能的。

　　He couldn't reasonably be expected to pay back the loan all at once.

　　公平合理地講，不可能指望他一下子歸還全部借款。

　　The award-winning novelist often has three or four books on the go at once.

　　那位獲獎小說家經常是三四部小說同時寫的。