选A是因为他是
独立主格结构句子是要有
谓语动词的,A选项中的fulfilled是
过去分词,having been fulfilled是动词fulfill的
现在分词的完成式的
被动语态,表示task和fulfill是被动关系,并且动作已经完成。就相当于after they fulfilled all the tasks ahead of time, ... 或 after all the tasks were fulfilled,...
如果选b,那就是一个句子,两个简单句不能用逗号连接,要加上相应的
并列连词,可以表达为
All the tasks had been fulfilled
ahead of time, so they decided to go on holiday for a week.
If the weather permits, we will go to the park tomorrow. 这是
状语从句Weather permitting, we will go to the park tomorrow. 这是独立主格结构,天气和允许是主动关系,用现在分词。
The homework finished, they went home. 独立主格结构,作业被完成,是被动关系,用过去分词。