Question

1,what is the reason for your not coming on time.

2,i really appreciate your offering to help me, but i am sure that i will be able to manage it by myself.为什么用your用you不可以吗

Answer 1

1. what is the reason for your not coming on time

   the reason for sth
   your coming  你来
   your not coming 你不来 都是事情的范畴

2. 1）appreciate sb/one's doing sth 感激某人做某事
   sb如果是代词，必须用宾格；one's指形容词性物主代词。
   2）appreciate it that从句

        i really appreciate you/your offering to help me都可以

      传统语法用your加上动名词，在口语或非正式语体中，常用宾格代替所有格。