[yòng xīn]
（集中注意力） diligently; attentively; with concentrated attention
do some hard thinking
用心去想一想
concentrate on one's studies; study diligently
用心學習
listen attentively to a lecture
用心聽講
work hard at exercises
用心做習題
have ulterior motives
別有用心
vicious intention
用心不良