“be＋过去分词”这个结构并不都是被动语态，也可能是系表结构。被动语态与系表结构主要区别是：被动结构表示一个动作，而系表结构表示主语的特点或所处的`状态，试比较下面的句子：
被动结构
The enemy was soon surrounded by us.
系表结构
The house is surrounded by trees.
被动结构
She was bitten by the dog in the darkness.
系表结构
I was excited by the news that my husband got promoted.
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