答案：C

题目分析：考查主语从句和强调句：这句话可以改成：That he is always addicted to video games makes his parents worried about him.所以判断是强调句，强调结构是：It is/was+强调部分+that+其余部分. 这里强调的是主语从句，he is always addicted to video games是完整的句子，用that引导主语从句，不做成分，that不能省略，句意：是他对录像上瘾使他父母对他很担心。选C。