新概念3册第5课最后一段话的语法结构分析请教？

Question

这是新概念3册的第5课中的最后一段话，原文是：
However, he had at last been allowed to send a fax in which he informed the editor that he had been arrested while counting the 1,084 steps leading to the fifteen-foot wall which surrounded the president's palace.
我的问题是：
1.counting为什么加ing
2.leading为什么加ing
2.surround为什么加ed

Answer 1

问题1，in which 引导一个定语从句，来说明传真的内容，因为内容是in the fax的，所以要用in which。
问题2，he had at last been allowed to send a fax是句子主干，in which 是定性定于从句修饰fax；which surrounded the president's palace是定于来修饰定于从句中的wall。本回答被提问者采纳