they have been looking forward是修饰the festival,所以对选项不起任何作用.讲解中是说，所属内容是时间状语从句的谓语动词，主句是将来时，从句是一般将来时。求解释when the festival (they have been looking forward to) comes这个部分是整个句子的时间状语从语，而people will dress up to celebrate it才是真正的主句。