(误)English is difficult to be learned.
(正)English is difficult to learn.(英语难学=学英语难，也可说It's difficult to learn English.原句的主语实际上是不定式的逻辑宾语，不定式要用主动形式。)
(误)He was laughed by all the pupils.
(正)He was laughed at by all the pupils.(不及物动词+介词=及物动词，变被动语态时介词不能省略。)
(误)They say him to have been rich.
(正)He is said to have been rich.(say后不可接不定式，但它的被动语态后可接不定式。)
(误)Tom asked me if these islands are belonged to America.
(正)Tom asked me if these islands belonged to America.
(误)He tried not to have mixed up in politics.
(正)He tried not to get mixed up in politics.(get作系动词，可代替be，后接过去分词表示被动，have无此功能。)
(误)Great changes have been taken place in China.
(正)Great changes have taken place in China.
(误)The war was broken out in 1937.
(正)The war broke out in 1937.(take place，break out，happen，belong to等不及物动词或短语动词没有被动语态形式。)
(误)I can't see the blackboard very well.Perhaps you need to examine your eyes.
(正)I can't see the blackboard very well.Perhaps you need to have your eyes examined.(表示使某物被别人…，通常使用have或get+物+过去分词表示。)
(误)They have married for two years.
(正)They have been married for two years.(表示已婚状态的持续，要用完成时的被动式。)
(误)He ordered the work to start at once.
(正)He ordered the work to be started at once.(不定式作宾语补语时，若与宾语是被动关系，要用不定式的被动形式。)
(误)The man thought to be a fool.
(正)The man was thought to be a fool.(主语是动作的承受者而不是发出者，用被动语态。)