英语的主动变被动They build houses every year.变成被动后：Houses are built

对的.直接放就可以了
一般主动变被动,有以下几种方法
1.把宾语当做主语,放到句首.
2.把原来的谓语改成be+过去分词的形式.（be要随时态和人称进行变化）
3.把原来的主语放到句末,并在前面加上一个介词by.
例如：
1.I ate three bananas yetserday.
2.She can cook dishes.
3.He gave me a new dress last week.
被动句：
1.Three bananas were eaten by me yesterday.
2.Dishes can be cooked by her.
3.
(1)I was given a new dress by him last week.
(2)A new dress was given to me by him last week.