Her motive was a genuine desire to improve conditions. 她的动机是真心想要改善状况。
+for The motive for the attack is still unknown. 袭击的动机仍然不明。
real/underlying/ulterior motive People thought he must have a ulterior motive for wanting to help. 人们认为他想提供帮助一定是别有用心。
question/suspect sb’ s motive When he visited her at home again, she started to question his motives. 当他再次到家里来看她的时候，她开始怀疑他的动机。