unless/ən'les/

conj. used to say sth will happen if sth else does not happen

conj. 除非：You will fail the exam unless you work harder. 除非你更努力些，否则你会考不及格的。

◇My little brother won't go to sleep unless Mom tells him a story. 妈妈不给小弟弟讲个故事，他就不肯睡觉。

音组-ess/-es/

assess; express; impress; possess; success; unless

用法unless引出的句子为条件状语从句，不用将来时。