once引导什么从句?
once
conj.一旦;一…就;当…时候。
adv.曾经;曾;一次;仅一次;(用于否定句、疑问句和if后)曾，根本。
She\'s planning to return to work once the children start school.
她正计划孩子一入学就恢复上班。
I\'ll run back over the procedure once again.
我将重新考虑这个程序。
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。
If necessary I can come at once.
如果有必要，我可以马上来。
A computer can perform many tasks at once.
电脑能同时做多项工作。