供参考^&^
第一个应该选A.
虚拟语气,主句用would + have done,从句用had done
第二个
In fact I have found it easy to read it.
前面的it是形式宾语,真正的宾语是动词不定式to read it,相当于
In fact I have found to read it easily.
found 和 read是两个动词,之间应该用to连接.
第三个
the idea of the reason “原因的想法”,of前面的idea才是先行词,要用that引导的同位语从句.