motivation ·noun (REASON)
Definition: the need or reason for doing something Level: C1
这次袭击的动机是什么？
What was the ___motivation for the attack?
虽然金钱是主要动机，但我遇到过许多人，他们为了获得相关经验而自愿工作，或者只拿更少的钱。
Although money is the main ___motivation, I have come across many people who have worked voluntarily or for less money to gain relevant experience.
理解他行为背后的动机对调查至关重要。
Understanding the underlying ___motivation behind his actions was crucial for the investigation.