Eg:The research is so designed that once_____ nothing can be done to change it.A begins B

问题描述:

Eg:The research is so designed that once_____ nothing can be done to change it.A begins B
having begun C begining D begun.Why choose

原因是横线上本来是一个省略句,句子本身是【once it's begun】一旦研究被开始
由于主语是it+be+过去分词的形式,因此可以省略剩下过去分词【begun】
翻译:这项研究设定好了,一旦开始任何事情都不能去改变它.