用心的学生

diligent student

用心准备功课

diligently prepare homework

用心学习

study diligently

用心听讲

listen attentively to the lecture

用心研究

research diligently

用心良苦

give much thought to something

用心险诈

have sinister intentions

险恶用心

sinister intentions

别有用心

have ulterior motives

无所用心

not give serious thought to anything

他的用心我完全知道。

I know exactly what his intentions are.