首先要强调的是,无论是ing形式还是过去分词形式,作用都是表伴随~之所以没有主语,是因为这句话的主语和主句的主语一致,所以省略了.第一句话中,如果把主语还原,该句为:Because he was devoted to his research, he spared no time to spend a weekend with us. (因为他把所有时间都花在了做调查上,所以周末没有时间陪我们)显然,两句主语一致,所以从句省略了Because he was,所以直接以devoted来开头;而第二句中,还原为Because she was to buy some salt, the careless housewife went downstairs, leaving the dish being cooked over the gas. (因为她想买些盐,所以粗心的妻子走下楼,可炉子上还有锅在烧着.)同理,两句主语一致,省略了Because she was ,所以该句以to buy 开头.所以,无论是ing形式还是过去分词形式都有表伴随作用.
动词的过去分词和现在分词做状语的某些区别.