With Halloween approaching, there exists a real concern among parents and teachers trick or treating will bee a seriously anti-social activity.
A. whether
B. what
C. that
D. how
网友回答
A. whether
B. what
(答案→)C. that
D. how
解析：考查名词性从句。句中that解释说明名词concern顾虑，担心，根据句意选C。