once的用法Once you have made a promise,you must keep it.这里once后

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once的用法
Once you have made a promise,you must keep it.这里once后面为什么要用完成时态,可不可以用其他的时态
如果是要表示将来的情况或者是虚拟的呢，例如这个句子Once he makes up his mind to do something no one can hold him back.

问题补充：
如果是要表示将来的情况或者是虚拟的呢,例如这个句子Once he makes up his mind to do something no one can hold him back.
这个是条件句：主将从现：
一旦你许了诺,就要遵守.
因为对现在有影响,而且发生在过去,所以要用完成时.

Once having made a promise,you should keep it. Once you ____ a promise,you must carry it out.A.have made B. Once you have made a promise ,you must carry it out.翻译 Once _a promise,you should keep it once you ____ a promise,you must carry it out. （）you have made a promise,you should cary it out.A.Once B.Un 23.Once you set a goal,you must _________ it. 状语从现填空:Once your promise ____(make),you will keep it without send me your address once you received it.句中once 后的receive用原 Once have.You'll rest Once you made adecision ,you should ____it . once you want,you must try to