Three men traveling on a train began a conversation about the world5 s greatest wonders.
“In my opinion,” the first man said, “the Egyptian pyramids (埃及金字塔）are the world’s greatest wonder. Although they were built thousands of years ago, they are still standing. And remember： the people who built them had only simple tools. They did not have the kind of machinery that builders and engineers have today. ”
“I agree that the pyramids in Egypt are wonderful，” the second man said，“ but I do not think they
are the greatest wonder. I believe computers are more wonderful than the pyramids. They have taken people to the moon and brought them back safely. In seconds, they carry out mathematical calculations that would take a person a hundred years to do. ’’
He turned to the third man and asked, uWhat do you think is the greatest wonder in the world?J, The third man thought for a long time, and then he said, u Well, I agree that the pyramids are wonderful, and I agree that computers are wonderful, too. However, in my opinion, the most wonderful thing in the world is this thermos. ” And he took a thermos out of his bag and held it up. The other two men were very surprised. “A thermos?” they exclaimed. “But that’s a simple thing. ”
“Oh，no，it’s not，” the third man said. “ In the winter you put in a hot drink and it stays hot. In the summer you put in a cold drink and it stays cold. How does the thermos know whether it1 s winter or summer?”

5、The third man was not very clever because____ .

A.he could not think of anything to say

B. he did not understand how a thermos works

C. he did not think the pyramids were wonderful

D. he did not know anything about computers