The problem with being a time waster is the online game playing often spills over into the periods of time that should be productive.
A. what
B. which
C. that
D. whether
网友回答
A. what
B. which
(答案→)C. that
D. whether
解析：本题考查名词性从句。句中that引导表语从句，在从句中不作任何成分，但在表语从句中不可以省略，故选C。