使役动词变被动语态时，需将主动语态中的不定式补足语还原为带 to的形式。以下是常见使役动词变被动语态的例子及解析：

一、常见使役动词（需加 to）

make

- 主动：She made him clean the room every day.

- 被动：He was made to clean the room every day.

let

- 主动：The teacher let the students write an essay.

- 被动：The students were let to write an essay.

have

- 主动：They had him finish the task.

- 被动：He was had to finish the task.

get

- 主动：She got him to call you last night.

- 被动：He was got to call you last night.

help

- 主动：They helped her with her homework.

- 被动：She was helped with her homework.

force

- 主动：The manager forced him to sign the contract.

- 被动：He was forced to sign the contract.

require

- 主动：The company requires employees to wear uniforms.

- 被动：Employees are required to wear uniforms.

allow

- 主动：She allowed him to use her car.

- 被动：He was allowed to use her car.

permit

- 主动：The manager permits late arrivals on Fridays.

- 被动：Late arrivals are permitted on Fridays.

二、特殊说明

感官动词（如see, hear）：

在主动语态中若使用 -ing形式（如 see sb. doing），被动语态需加 to（如 be seen doing）。

情态动词（如can, may）：通常不用于被动语态，需通过其他结构表达（如 be made to do）。

三、注意事项

省略的 to 必须还原：

例如主动语态 have sb. do sth.的被动语态为 be made to do sth.，而非 be having to do。

强调动作承受者：

被动语态可突出动作的接受者，如 The experiment was conducted by the team强调实验由团队完成。

通过以上规则和示例，可系统掌握使役动词的被动语态用法。