one little question about english

题目

one little question about english
The seasonal nature of the industry’s work demanded that the timing of training courses ________ carefully selected.A) wasB) had beenC) beD) were
为啥是C?
类似的词都有哪些呢？希望全一些，

答案

demand这一类表要求、命令的动词出现时,后面的宾语从句常用虚拟语气should do,should 可省略
虚拟语气用在 suggest,demand,insist,ask,move,advise.desire,order,propose,require,recommend,request,maintain,vote 等表示建议,命令,请求的动词后的宾语从句中,从句的谓语用 should + 原形动词,但美国英语中常要省去 should .