(give)—more instruction,thestudents would have done the exer
(give)—more instruction,thestudents would have done the exercisemuch better答given (give)—more instruction,the students would have done the exercisemuch better答given为什不是虚拟if had given
the students would have done the exercisemuch better 显然是虚拟 因为主语是the students,前面一定要被动, 可以说:given 或者不用分词短语,改成复合句的分句. if they had been given, if had given这样不行.