She is never completely sincere in what she says about people.

　　她談?wù)搫e人，一向不盡坦誠(chéng)。

　　She was sincere and genuine in her wish to make amends for the past.

　　她誠(chéng)懇而真心地希望彌補(bǔ)過(guò)去的錯(cuò)誤。

　　I am writing to express my sincere gratitude for your help in my study.

　　我寫(xiě)這封信是為了感謝你在學(xué)習(xí)上對(duì)我的幫助。