这是新概念3-36课：

When I was a boy, my grandfather told me how a German taxi driver, Franz Bussman, found a brother who was thought to have been killed twenty years before. While on a walking tour with his wife, he stooped to talk to a workman.

After they had gone on, Mrs. Bussman commented on the workman's close resemblance to her husband and even suggested that he might be his brother. Franz poured scorn on the idea, pointing out that his brother had been killed in action during the war.

Though Mrs. Busssman fully acquainted with this story, she thought that there was a chance in a million that she might be right.

1)After they had gone on - 这句话没看懂在课文中go on指的是什么？为什么不用一般过去时呢？that she might be right 同位语从句的先行词是整个a chance in a million 还是单个的 a chance 呢？

A few days later, she sent a boy to the workman to ask him if his name was Hans Bussman. Needless to say, the man's name was Hans Bussman and he really was Franz's long-lost brother. When the brothers were reunited,

Hans explained how it was that he was still alive.

2) How it was that he was...强调句？但感觉how句意不通，用why更好理解？！

After having been wounded towards the end of the war, he had been sent to hospital and was separated from his unit. The hospital had been bombed and Hans had made his way back into Western Germany on foot. Meanwhile, his unit was lost and all records of him had been destroyed. Hans returned to his family home, but the house had been bombed and no one in the neighbourhood knew what had become of the inhabitants. Assuming that his family had been killed during an air raid, Hans settled down in a village fifty miles away where he had remained ever since.

3) 以towards the end of the war 为过去时间点，之前发生的事件使用过去完成时，那么was separated 为什么不使用过去完成时呢？

而The hospital had been bombed 和 Hans had made his way back 这2句话使用过去完成时又是参照哪个过去时间点或过去动作呢？

4）his unit was lost and all records of him had been destroyed.- 为什么不是had been lost？all records of him had been destroyed - 这个过去完成时含义呢？

谢谢老师！