你说的对,because应该改成that.
后面的that makes life worthwhile 是一个定语从句,是正确的.
全句是：The most importnat reason why governments should support art is that an appreciation of art is one of the things that makes life worthwhile.我有点搞不清that makes life worthwhile 是修饰 things的还是修饰appreciation的，如果是修饰things的就应该把单三改为 that make 吧？你又说对了，that make life worthwhile 是修饰先行词things 的，因此，makes 应该改成make.是我粗心了。