阅读短文，根据短文内容，从短文后的五个选项中选出能填入空白处的最佳选项。每个选项只能用一次。
Careful and careless are as different as fire and water. But it is strange that quite a few scientists have both these qualities (品质 ). They are both careful and careless. .
Once Newton invited a friend to dinner at home. When they were ready to eat, Newton left to get a bottle of wine (酒). , Newton still didn't come back. At last his friend found Newton in his lab. When Newton was going to get the bottle of wine, he suddenly had a new idea for his experiment. So he quite forgot his friend and the dinner. Another time, Newton was leading a horse up a mountain, and he held the rein(缰绳) in his hand. While he was walking along, he kept thinking about problems. , he found that the horse was gone.
Einstein was another example. . While waiting, he became lost in thought. It started to rain. The rain kept on for some time. When he took out a piece of paper to write something down, the paper was wet and then he knew that it was raining. , he again forgot he was standing in the rain.
A. But after he put the paper into his pocket
B. But after his friend had waited for a long time
C. Once he was waiting for a friend at a bridge
D. Newton, the famous English scientist, was such a person
E. When he got to the top of the mountain