问题补充：
It is beneficial for us to do morning exercise.还是It is beneficial to us to do morning exercise.beneficial怎么用,是to sb 还是for sb.像 Sunlshine is beneficial to plants这里是用to 的.
答案：
It is beneficial for us to do morning exercise.正确
======以下答案可供参考======
供参考答案1:
因为有一个固定搭配：it is加adj(for sb.)to do sth.其中的it是形式主语，真正的主语是to do sth.然而Sunlshine is beneficial to plants中并不是这样，这里面是be beneficial to do stn.
供参考答案2:
用for.
