问题
选择题
Nowadays，it is common 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
答案
答案：D
题目分析: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。