题目

A Bite of China Season Two(《舌尖上的中国 》第二季)  is coming! The program is shown at 9 : 00 on CCTV-1 every Friday night fr om April 18 to June 6, 2014. There are altogether eight episodes (集), all about history and culture of food, eating and cooking in China. The directors spent one year visiting more than 150 different parts of China. More than 300 types of food are covered in the documentary. As an old Chinese saying goes, food is what matters most to people. It plays an important role in our daily life, and the rich food culture is also one of the most important 函数y=x-23，自变量x的取值范围是______．