People were visiting a museum in a city. Suddenly, all the lights inside the museum went out. A moment later, the lights were turned on again.
At the same time, a basket flew out of the window. There was a painting in the basket! It was the Girl With a Pearl Earring (《戴珍珠耳环的少女》). It's a famous painting by Johannes Vermeer. But a painting that looked the same was still on the wall of the museum. The museum manager checked the painting on the wall and said, "The one in the basket is real. A thief changed the painting! Let's call the police."
A detective (侦探) came. He called the guards in the museum together and asked, "Do you have an alarm here?"
"Yes. And it rings when someone moves the picture，" one guard said. "Only our manager can move it. He has the key."
But the alarm didn't ring. "Does the alarm need electricity?" asked the detective, "Yes," said the guard.
The detective touched the painting on the wall carefully. His hands got some paint from it. Then he checked all the guards' clothes. There were some paint on a guard's clothes. "He is the thief, " the detective said.
Do you know why?
