题目

Here in Siberia（西伯利亚），the winter is always very long and it's very，very cold! It starts to snow in November and the snow won’t leave until May．The temperature is usually about-25℃，but it's sometimes much colder．When it's-35℃, children can’t go to school，but adults still go to work! We wear a lot of warm clothes，socks and boots（靴子），sweaters and fur coats．All the houses have heating（暖气），so it is never cold inside．In winter, we close all the windows to stop the wind from getting in and we don’t open them again until spring． In spring a 如图，点D，E，F分别是△ABC三边上的中点．若△ABC的面积为12，则△DEF的面积为________．