My mother gave me a present for my birthday.（改为被动语态）
A present was given to me by my mother for my birthday.
或 I was given a present by my mother for my birthday.
give是接双宾语的,所以这句有两种改法.一种是物（礼物）作主语,一个是人（我）作主语.时态是过去时,主语都是单数,所以谓语结构由was加上过去分词given构成.原来的主语由by来表示.