① This includes parties, concerts and discos in the institute and trips to the theatre, museums and sporting events in London.

【答】the theatre, museums and sporting events：这些词语并列，说明：the theatre表示“类别”，相当于复数的theatres。英语中，单数theatre经常跟the连用，表示“类指”和复数概念。例如：

You can move up to work in films and the theatre.  

你可以转行从事影视戏剧业。

来自柯林斯例句

 ② We all know that it is young people who generally provide the labor force, new ideas and energy for the modern society.

【答】“现代社会”的英语是： modern society，不加冠词，所以本句应删掉the。

 ③ Older people may still play an important role in the modern society.

【答】道理同上。“现代社会”的英语是： modern society，不加冠词，所以本句应删掉the。