We have heard of many cases some citizens ，especially some famous people， have suffered because personal information had been leaked.
A. why
B. which
C. as
D. where
网友回答
A. why
B. which
C. as
(答案→)D. where
解析：定语从句的先行词cases在此意为“实例，情况”，根据从句的意思“在这些例子中（情境中）……”，先行词在从句中应该担当状语成分，表示in many cases，所以用where 来引导表示地点的定语从句。