阅读短文，从方框中选择合适单词并用其适当形式填空。
| or, be, at, look, find, it, try, some, never, also |
We call them aliens (外星人) or sometimes ETs (extraterrestrials) we make movies about them, even though we have seen them. We don't even know whether they are real or not. But we never stop for them.
The universe(宇宙) is a big place. Scientists say there many planets outside our solar system (太阳系). It is very possible that smart forms of life, aliens are living out there.
Scientists are many ways to find aliens. They use radio telescopes (无线电天文望远镜) to search (搜寻) the sky for alien signals (信号). They send radio messages and signals into deep space. They hope aliens will find their messages and answer.
But after years of searching, we haven't heard alien messages yet.
Some scientists say they might not any aliens at all! They think that Earth came into being by chance(偶然地). All the right things came together the right time and formed life on our planet. They think would be too hard for this to happen again.