D
If aliens ever sent us a message,scientists hope to pick it up in a distant part of northern California.
There,in a place among the volcanoes of the Cascade Range,42 radio dishes point together at the sky. The dishes,each 20 feet across,form a single,huge scientific instrument called the Allen Telescope Array. Scientists built them to receive radio signals— the sort of message that could answer a very important question： Are we the only intelligentlife in this vast universe?
“It's a question humans have been asking forever,” observes astronomer Jill Tarter. Until recently,she led the SETI (Search for Extra-Terres-trial (外星的) Intelligence) ，Institute in Calif. “We read these ancient texts,and the ancient Greeks,the Romans,the Chinese —they were all wondering how we humans fit into the universe. ”
While the question is ancient,our understanding of the universe has changed over the centuries. We now know that stars do not hang from the sky like fruit on a tree. We also know Earth moves around the Sun and not the other way around. But we still don't know if life exists elsewhere. If aliens do exist,does it have the technology to communicate with us on Earth?
If so,the Allen Telescope Array is listening,day and night,for some signal. From time to time,the dishes turn toward a new patch of the sky. The array has not yet picked up any alien calls.
But that has hardly frustrated scientists. The search for life elsewhere in the universe continues to prove irresistible (无法抗拒的) to experts in a wide variety of fields,from biology to astronomy,and from psychology to computer science. And they’re not just looking for aliens that can communicate： Many researchers believe that simpler,microscopic alien life might be hiding on some distant planet.
Even if their search has yet to turn up any aliens,it has led to some surprising discoveries —including some right here on Earth. If anything,the search for extraterrestrial (外星人) life has become a lot more exciting. Perhaps it's just a matter of time until we discover we’re not alone.
51. Why did scientists build the Allen Telescope Array?
A. To keep a record of the volcanoes.
B. To pick up messages from aliens.
C. To send up radio signals.
D. To keep in touch with aliens.
52. From what Jill said,we know ancient people.
A. described the existence of aliens in texts
B. compared stars to fruit on a tree
C. didn't believe humans to be alone
D. didn^ know how to fit humans into the universe 53. It is implied in the sixth paragraph that .
A. aliens may live in many different places
B. aliens like to hide in a secret place
C. aliens may understand the science of astronomy
D. aliens may not have the ability of communication
54. The writer's attitude towards the existence of aliens was.
A. positive B. doubtful
C. neutral D. disapproving
55. The main idea of the passage is that.
A. humans are not alone at all in the universe
B. scientists search for aliens in space
C. alien calls haven’t been received so far
D. California is a base to welcome aliens
