reason有时要用复数
如"There are reasons for this great interest in the ideas,feelings,and actions of youth."
"对年青人的思想、感情和行动发生这样巨大的兴趣,自有它的道理."
第2个问题可以这样理
你把句子还原马陈述句,即
Karen Marsh gave reasons for which he wants to retire.
可见give for wanting to不是词组
原句reasons是give的宾语,for后面给出原因