The police still not sure the young man killed himself or was killed.
A. is, if
B. is, whether
C. are , whether
D. are, that
网友回答
A. is, if
B. is, whether
(答案→)C. are , whether
D. are, that
解析:if是否,如果;that因为,以至于;whether是否;weather天气。警方还不确定这个年轻人是自杀还是他杀。If和whether都能表示是否,但是whether常和or搭配使用,本句中police为集合名词,表示复数含义,故选C。