diffident

他在面试中显得缺乏自信，犹豫要不要谈论自己的成就。

He appeared ___diffident during the interview and hesitated to talk about his achievements.

他有气无力的握手透露出他在社交场合缺乏自信。

His ___diffident handshake suggested he lacked confidence in social settings.

获奖后，她发表了一通怯生生的感言，让所有认识她的人都吃了一惊。

After receiving the award, she gave a ___diffident speech that surprised everyone who knew her as confident.