英语关于时态的道题

all the tasks(having been finished)ahead of time是一个状语从句，不是单独的句子，用来修饰后面的they decided to go on holiday for a week 。在英语里面，一个句子只能有一个主语一个谓语。所以have 是非谓语动词，要变形。而all the tasks对于have来说是施事，所以have加ing

因为前后的两个主语不一致，而且他们是用都好隔开的，而不是and

呵呵，这是一句话，前边的all the tasks(having been finished)ahead of time为表示原因的，它就等于：Because all the tasks had been finished ahead of thime, they decided to go on holiday for a week.
或者All the tasks had been finished ahead of thime, so they decided to go on holiday for a week.

if use "had been finished", 那么，两个分句就没有任何逻辑联系。中间要用句号。
all the tasks having been finished ahead of time独立主格结构作状语
相当于连词，关系代词等。两个分句就有逻辑联系了