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Explanation: 在陆谷孙主编的《英汉大词典》第二版（上海译文出版社）第1864页，sign词条下的vi.搭配中，有sign off这一项，下列八个义项，其中第二义项为“（使）脱离关系；解雇”，第三义项为“离开；退出（活动）”。
a. to withdraw, as from some responsibility or connection.
b. to cease radio or television broadcasting, esp. at the end of the day.
c. Informal. to become silent: He had exhausted conversation topics and signed off.
d. to indicate one's approval explicitly if not formally: The president is expected to sign off on the new agreement.
rockyhon Australia Local time: 22:22 Meets criteria Native speaker of: Chinese