she was dressed in white and looked very beautiful这句有一并列谓语.即 was dressed in white and looked beautiful.句子是一简单句.可改为she looked very beautiful dressed in white.这句中的dressed in white 是过去分词短语做原因状语.也可改成一有原因状语从句的复合句.相当于
She looked very beautiful because she was dressed in white.状语从句中的主语she和主句中的主语是同一人.所以从句中就可把前面的词省略掉.即省略了because she was.而用了过去分词做状语.再如 Tired of the speech, he went out of the hall.