I wonder what her motive was in breaking the windows?
书上原句。
我觉得应该用for, for breaking the windows.
请教老师剖析！
原句没错。a motive for sth, a motive in doing sth.
《韦氏高阶》例句：Theirmotivein running away was to avoid being punished.
No one knows the main/real/underlyingmotive forhis behavior.