Maggie, Travis and Lucy's science teacher set a special test for them. They had to work out different kinds of problems within limited time to get out of a locked room.

For the past hour, Maggie, Travis and Lucy had been locked inside a room decorated like a mad scientist's laboratory. Together they decoded（破译）a secret language and solved a difficult maths problem.

The last challenge, however, stopped them. The key to the door was trapped in a block of ice. 

"We have to melt the ice," Lucy said.

"But there's nothing hot here!" Maggie complained.

Travis pulled off his sweatshirt and wrapped（裹）it around the ice. "This keeps me warm," he reasoned.

A few minutes passed by, but the ice didn't melt.

"Isn't cloth an insulator（隔热材料）?" Lucy asked. She tried to remember what she had learned in science class. "Heat always flows from warm objects to cold ones. The heat in the air will eventually melt the ice, but we need to find something that will help heat move from the air to the ice more quickly."

"What about glass?" Maggie asked.

"Glass is also an insulator. It keeps heat from moving," Lucy said. Then she noticed a large metal tray（金属托盘）across the room. "This might work!"

Lucy put the block of ice onto the tray. Everybody's eyes moved between the clock and the ice. Would they be able to free the key in time?

At last, the key lay in the water on the tray. The three friends rushed out of the room in the last minute. 

"We made it!" Travis cheered. "Good thing you paid attention in science class!"