选C是对的, 因为你是观看的是电影, 只要你的眼睛没问题, 就不会有difficulty. 至于观看的效果是高兴的还是沮丧的（disappointing), 就由你自己判断了.
这里主要是对英语单词的理解和对词性的分析.
如果题目是: He finds reading this part of English ___ because so many new vocabularies
就可以填 difficult.
下面的情况也可以填difficult
He finds watching the movie ____ because he is shortsighted