delight in 和delight at的区别,

delight in 从...取得乐趣 （表示目的,意图）
delight at 因 ...而高兴 （表示因果关系）
意思和用法的不同可以从下面例句看到：
John delights in playing practical jokes on his friends.
Mary delights in going for long walks in the park.
He delights at the thought of finally making it to Harvard.