Novel way to escape heat

As most parts of China enter the hottest season of the year, some Chongqing residents have discovered a novel way to escape the heat: Play mahjong in a cave. The temperature inside the cave was 20 degrees Celsius, while the outside temperature hovered over 30 degrees Celsius all day long.

What is the temperature inside the cave?

A. 12℃

B. 30℃

C. 20℃

（中国日报网英语点津 Helen 编辑）