They included detailed drawings of the human body,plans for engineers to build canals and bridges,an

题目

They included detailed drawings of the human body,plans for engineers to build canals and bridges,and astonishing drawings of machines which were not to be built until hundreds of years later,such as aeroplanes,parachutes,submarines and tanks中were not to be built为什么要加to

答案

注意句子后面跟的 until hundreds of years later,这句是"将来时"被动语态的写法.
which 引导的定语从句指代 machines,were not "to be built" until ...意思是这些机器有图纸但直到数百年之后都 “还不会被建造”.
对当时而言,确实是很久远之后才会发生的事,所以用将来时.
被动语态的基本句式是 be 动词 + 动词过去分词,还得根据语境做出时态上的调整.
基本的时态如下（以你例句中的动词 “建造” build为例）：
现在时：(is/are) built
过去时：(was/were) built
将来时：to be built
完成时：have/has/had been built
进行时：is/are being built