The policeman is still not sure the young man killed himself or was killed.
A. if
B. that
C. whether
D. weather
网友回答
A. if
B. that
(答案→)C. whether
D. weather
解析：if是否，如果；that因为，以至于；whether是否；weather天气。警察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，联系下文可知选C。