单项选择题

E

Careful and careless are as different as fire and water. But strangely enough many scientists have both these qualities, that is, they are both careful and careless. Newton, the famous English scientist, was such a person. Once Newton invited a friend to a dinner at home. When they were ready to eat, Newton still didn’t come back. Finally his friend found Newton in his lab. The reason was that when Newton was going to get the bottle of wine, he suddenly had a new idea for the experiment he was doing, so he completely forgot his friend and the dinner. There was another time when Newton was leading a horse up a mountain, holding the rein (缰绳) in his hand. While he was walking, he kept thinking of problems he had met in his studies. When he got to the top of the mountain he found that the rein was not in his hand and that the horse was gone. Among scientists, there are many people like Newton. Einstein was one. Once he was waiting for a friend at a bridge. While waiting, he became lost in thought. It started to rain. The rain kept on for some time. When Einstein took out a piece of paper from his pocket to write something down, the paper was wet and then he realized that it was raining. His clothes had become completely wet. But after he put the paper into his pocket, he again forgot he was standing in the rain. Many scientists are careless about how they live. This is because they are too careful in their studies.

Once Einstein was waiting for a friend at a bridge when it started to rain. He stood there and______.