I failed in the end ,though he tried everything he could __ me

题目

I failed in the end ,though he tried everything he could __ me
A to help B helped C help D helping

答案

选A
句意为尽管他已经做了所有他能做的来帮我.
he could是everything的定语 ,是嵌套在try to do 里的,所以help 的形式与could 无关