主动语态怎么转变成被动语态

比如

i am doing my home work - am doing
my home work is done by me - is done
宾 + BE + 过去分词 + （BY 主语）有时会省略如：
my work is done.

补充一下：就是省to不定式在变成被动时要加to.
for example:i made her be unhappy.------she was made to be unhappy(by me)

一般是宾语＋BE动词＋过去分词＋BY＋主语