根据短文内容，选择正确答案。

     Feeling sad? Go shopping, because it really can make you happy again.

Scientists interviewed hundreds of shoppers at shopping centers, and they asked them to keep diaries of their shopping trips. The people who were unhappy on their way into a shop, they all became happy after the shopping. This is called “retail therapy”.

     Shopping is good for your health. Walking between shops and carrying heavy shopping bags burns 385 calories(卡路里) a week for a British woman, according to a study. The study tested 10 shoppers—five men and five women. It found that women cover an average of nearly three miles during the 2.5 hours they spend walking in me shopping centers every week. But men spend just 50 minutes shopping and cover just 1.5 miles.

物体保温要尽可能加快热的传递，选用的材料应该是热的____。