题目内容：

非谓语英语选择题
Whle Mr.Yang was examining the composition his son had finished____the possible spelling mistakes in it,the mistakes he got used to____ him a lot.
A.to correct；annoying
B.correcting；annoyed
C.to correct；annoyed
D.correcting；annoying
请问第二个空为什么用过去分词呢?并请分析一下句子结构,