A、By looking through the keyhole. B、By looking through the window. C、By taking pictures of the monkey. D、By hiding himself behin

A university professor recently made several experiments with different animals to find out which was the most intelligent. He found out that monkey was more intelligent than other animals.
    In one experiment the professor put a monkey in a room where there were several small boxes. Some boxes were inside other boxes. One small box had some food inside of it. The professor wanted to watch the monkey and to find out how long it would take the monkey to find the food. The professor left the room. He waited a few minutes outside the door. Then he knelt down and put his eye to the keyhole. What did he see? To his surprise he found himself looking directly into the eye of the monkey. The monkey was looking at the professor through the keyhole on the other side of the door.