英文: Attendance is purely voluntary.
中文: 这次出席纯粹是自愿的.英文: She does voluntary social work.
中文: 她从事义务社会工作。英文: They are all voluntary workers.
中文: 【他们都是自愿的义工。】英文: Charities rely on voluntary donations.
中文: 慈善事业依靠自愿捐献。英文: The marriage must be voluntary.
中文: 婚姻必须是自愿的。