Read the passage and choose the correct answer to each of the questions:


Is there intelligent life on other planets? For years, scientists said "no" or "we don't know". But today this is changing. Seth Shostak and Alexandra Barnett are astronomers. They believe intelligent life exists somewhere in the universe. They also think we will soon contact these beings.

Why do Shostak and Barnett think intelligent life exists on other planets? The first reason is time. Scientists believe the universe is about 12 billion years old. This is too long, say Shostak and Barnett, for only one planet in the entire universe to have intelligent life. The second - the universe is huge. Tools like the Hubble Telescope "have shown that shown that there are at least 100 billion galaxies," says Shostak. And our galaxy, the Milky Way, has at least 100 billion stars. Some planets circling these stars might be similar to Earth.

Until recently, it was difficult to search for signs of intelligent life in the universe. But now, powerful telescopes enable scientists to identify smaller planets - the size of other solar systems. These planets might have intelligent life.

Have beings from space already visited Earth? Probably not, says Shostak. The distance between planets is too great. Despite this, intelligent beings might eve other methods, such as radio signals. In fact, they may be trying to communicate with us now, but we don't have the right tools to receive their messages. But this is changing, says Shostak. By 2025, we could make contact with other life forms in our universe.

According to Shostak, what might prevent beings from space visiting our Earth

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