Question

It was childish ____ her to argue with her little brother. A: for, B: on, C: of,

Answer 1

It was childish （ of ）her to argue with her little brother. 这句话的真正主语是动词不定式复合结构 （of ） her to argue with her little brother.用of 还是用for, 关键是看课和前面的形容词 childish能否有逻辑上的主表关系? 可以说 she is childish.用of, 否则用for。

Answer 2

选 C.of
childish 是表示某人的品质的形容词

It was childish of her to argue with her little brother.