1. the Beijing Opera（用定冠词）

Li Zhen: How did you like the Beijing Opera yesterday?

David: Wonderful! I have read about the Beijing Opera online.

以上两句中的 the Beijing Opera 之所以加了定冠词，是因为这里的 Beijing Opera是指具体的京剧节目，且为特指——the Beijing Opera yesterday 意思是“昨晚的京剧”。

2. Beijing Opera（不用定冠词）

How would you introduce Beijing Opera to someone who doesn't know about it?

上面句中的 Beijing Opera 之所以没有加定冠词，是因为这里的 Beijing Opera是指笼统意义的京剧，且为非特指，所以不加定冠词。

相关解答可参考：

https://www.cpsenglish.com/question/55537