樓主說的可是過去分詞做狀語表示被動的情況?如果是這種情況,則可以不用be動詞,
e.g.He may not come to the party tonight,forbidden to go out by his parents.
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如果是兩個動詞同時充當謂語表示并列,而后一個動詞又有被動的意思,那麼要視前一個動詞是否使用be動詞而定,
1.前一個動詞使用be動詞,但是不是表示被動,則后一個動詞必須要加be動詞
e.g.She was insisting writing out the truth while was told to stop by some politicians.
但是這句話最好講成：While told to stop by some politicians,she was insisting writing out the truth.把后一個動詞變成狀語放在句首.
2.前一個動詞使用be動詞,同時示被動,則后一個動詞可省略be動詞
e.g.This photo was found in the dustbin and then sent to the FBI.
3.前一個動詞不使用be動詞,后一個動詞如果表示被動則需要加上be動詞
e.g.This guy stole the precious vase and was caught by the cops a month later.