Nowadays，it is mon to see people staring at their mobile phones instead of reading a real book，＿＿＿＿＿＿many experts are worried．
A. when
B. for which
C. where
D. about which
网友回答
A. when
B. for which
C. where
(答案→)D. about which
解析：
试题分析:句意：如今经常看到人们盯着他们的手机而不是读真正的书籍，对此很多专家非常担忧。在非限制性定语从句中be worried和介词 about构成短语，which指代前面提到的情况，所以选D。