被动的结构是 be动词+动词的过去分词.
比如： They built the house. 这里用的是built,be动词要用过去式
The house was built by them.
The dog ate the bone. --->The bone was eaten by the dog.
She waters flowers every day. ---> The flowers are watered by her every day.
看明白了吗? 前面两个是过去时的被动,后面一个是一般现在时的被动.
其实最典型的例子是： I was born in Ningbo. 我出生在宁波.这里的出生其实是被生.