一道高中英语选择,求原因,

问题描述:

一道高中英语选择,求原因,
He is ready to help others,seldom ,-----------,refusing them when they turn to him
a if so
b if possible
c if not
d if ever

选D,if ever是一个短语,为if there is ever的省略形式,there is ever,是“如果有也是少见的,几乎从来不”的意思.
句子的意思是:他很乐意帮助别人,当有人求他帮忙时,他几乎从来没有拒绝过.