这里有一个句子：Whatparentsneedtodoispraisetheirchildrenforgoodbehaviour.类似的,whatweshoulddoistryourbesttodoourcurrenjob.为什么is后不用v-ing形式而用原形?提取主干难道不是what……isdoing?还

Question

这里有一个句子：
What parents need to do is praise their children for good behaviour.
类似的,what we should do is try our best to do our curren job.
为什么is 后不用v-ing形式而用原形?提取主干难道不是what……is doing?
还是is 后省略了一个to?如果是,为什么要省略?涉及何种语法?
另外,还有一个类似句子：
what we should be doing focusing on the job we are currently in now.
为什么此处is 后用v-ing形式?
抱歉，第二句漏掉了is
应为what we should be doing is focusing on the job we are currently in now.

Answer 1

语法上成分要求前后一致,前面用了 doing,后面的用doing; 前面的用 to do;后面 的用 to do
第一个问题,这里是省略了to;因为前面有实意动词 do,所以可以省略 to; 否则不能省略to
what we should do is to try our best to do our current job better.
what 结构做主语,习惯上也用不定式作表语的.
第二题问题,你漏掉了is吧.
语法上来说,不定式和动名词都是可以作表语的.也不做区分.这里是为了结构的平衡,用动名词更好一些.