4)主动句变被动句的基本句式：

a) 主：主语+助动词(情态动词)+谓语+宾语

被：主语(原宾语)+助动词(情态动词)+be+动词过去分词+by+原主语

如，We will help him.→He will be helped by us.

主：主语+动词短语+宾语

被：主语(圆宾语)+be+动词短语的过去分词+by+原主语

如，They looked after the babies.→The babies were looked after by them.

主：主语+谓语+间接宾语+直接宾语

被：主语(间接宾语)+be+动词过去分词+原直接宾语

主语(直接宾语))+be+动词过去分词+to(for)+原间接宾语+(by+原主语)

如，We gave him some magazines.→He was given some magazines.

Some magazines were given to him by us.

【注意】一般将主动句中表示人的间接宾语变为被动句中的主语。

主：主语+谓语+宾语+宾语补足语

被：主语(原宾语)+be+过去分词+原宾语补足语

如，They elected him their monitor.→He was elected their monitor.

【注意】如果主动句中宾语补足语是不带to的不定式，变成被动语态后一般要加to.

I saw him go to the church.→He was seen to go to the church.

【扩展】一般在以下几种情形时，需要使用被动语态。

不知道动作的执行者，只知道动作的承受者时。

When we got there, the room had been cleaned already.

不必要说出或出于礼貌不便说出动作的执行者时。

I was told that you were not honest enough.

3)有必要突出或强调动作的承受者时。

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