将下列句子变为被动语态每空一词，求助，（语法详细）

1. are made  to work 这里要用到被动语态，那么就是be+动词被动式+to do sth, 所以前面的make-made, 后面的work 保持原型,另外这句话是一般时态，所以前面be动词用了are
   

2. 也是一样的，were seen to play ,这句话是过去式，所以是 were
   

he makes the farmers work for a long time.
The farmers__. __.__.__for a long time.
为什么填are made to work

凡是主动的时候省略to 的，比如三个使役动词，还有see sb do sth之类，被动的时候要把to 加上

2.I saw them play football on the play ground.
They _were _._seen _.__to.__.football on the playground.

你还少写了个were,道理同上，重点就是主动的时候不加to,被动要加to

然后，第一题的he 和第二题的they ,变成了by him 和by them ,可以省略

理由是：
感官动词和使役动词：如果后面用的是动词原形，被动语态都要加to。

were seen to play