Moviegoers know that many special effects are created by computers, they often don' tknow is that these scenes still require a lot of work.
正确答案： C
本题解析：
【考情点拨】考查主语从句引导词。
【应试指导】句意：常看电影的人知道很多特效都是通过电脑制作出来的。但他们往往不知道的是制作这些场景还需要投入大量的工作。分析句子结构可知，空格所在从句在整个句子中充当主语，从句中缺少宾语，且宾语指的是事而非人，故选 C。
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