求详解once begun还是once beginning?The research is so designed that once begun,nothing can be done to change it.我知道此处是省略了once (it is )begun,但once beginning

求详解once begun还是once beginning?The research is so designed that once begun,nothing can be done to change it.我知道此处是省略了once (it is )begun,但once beginning The research is so designed that once _______nothing can be done to change it.A. begins B. having begun C. beginning D. begun求详解.waiting once! once once Once once Once once once once once completed用法和once it completed 的用法··如once published ,the dictionary will be popular可以改成once it published 或者once it is published ```这句子是考查非谓语动词还是时态什么的··求详解 The research is so designed that once begun nothing can be done to change it.The research is so designed that once begun nothing can be done to change it.为什么是once begun 为什么不是once begin.once negun=once itis begun那算被动语态了 求once同义词一次是a time还是one time Once _a promise,you should keep itA.having made B.making求详解 try again 等于once more还是try once more The research is so designed that once begun nothing can be done to change 英语改错：Once to be begun,the plan will never be changed 哪里错了?