It is strange that they----touch with each other for ten yea

选A正确.
因为,首先,有虚拟语气的固定句型：
It +be +necessary/strange/natural/important that sb should do sth.
其次,should have done,表示【过去本来应该做某事（却没有做）】.按照句子意思,这里需要表示的意思是【他们竟然失去联系长达十年】.
祝你开心如意!