reticent
adjective formal uk/ˈret.ɪ.sənt/ us/ˈret̬.ə.sənt/
沉默寡言的;不愿交谈的
unwilling to speak about your thoughts or feelings
He is very reticent about his past. 他不愿谈及他的过去。
Most of the students were reticent about answering questions. 大多数学生都不愿回答问题。