It is cruicial that the plan ( ) at once

问题描述:

It is cruicial that the plan ( ) at once
A ve worked out B.is worked out C work out Dto be worked out 说出理由

答案为A;
已知这里It 作形式主语,真正的主语为从句,the plan.
另外由选项我们可以知道,从句的意思是:这个计划(应该)马上被执行.
整个句子的意思是,这个计划须马上执行至关重要.
由此我们可以得知,整个句子是:It is cruicial that the plan (should)be worked out at once.
should 表虚拟语气,可以省略.故选A.
注:有很多此类句子,省略should的.
例如:It is the time you (should) go to bed.