The nurse won't leave her patients ____ she's sure they are all taken good care of.
A. if B. because C. since D. unless
【答案】D
【解析】句意：护士不会离开她的病人，除非她确定他们都得到了很好的照顾。考查连词辨析题。A. if如果，表条件；B. because因为，表原因；C. since由于/既然，表原因；D. unless除非，表条件。本句是条件状语从句，可排除BC两项。if意思与句意不合，可排除。根据句意，故选D。