شرکت در آزمون آنلاین زبان انگلیسی 2 - زبان انگلیسی 2 | آزمون شماره 6447

Because of some visa problems, I could not say goodbye to my family ................ I should call them as soon as I land in Tajikistan.

Can you bring me a one-liter … of water, please?

For thousands of years, humans have explored the Earth. Nowadays, we are exploring space. Astronomers are the modern-day explorers who study the stars and planets. Currently, many astronomers are looking for new planets and new places for humans to live in the future. But where do astronomers start looking?

   First of all, astronomers look for a star. That’s because our own Earth orbits a star (the Sun). More importantly, it is in the correct distance from the Sun for heat and light. So when astronomers have found the star, they look at the planets around it. In recent years, astronomers have found nearly 400 new planets with stars. Unfortunately, many of these planets are either too near to the star or too far away.

   However, if the planet is in a good position, astronomers look for three key things: water, air, and rock. Water is important because life needs water. Humans can drink it and they can also grow plants with water. And plants produce air to breathe and food to eat. So all life on other planets will need water and air. Rock on a planet is also important. That’s because there is often water under the rocks.

   After many years of searching, astronomers have found a planet that is similar to Earth. It’s Gliese 581g and it’s near a star. The astronomers think it has water and rock and its average temperature is between –31°C and –12°C. That’s cold, but not colder than Antarctica or the Arctic Circle, for example. Gliese 581g is bigger than the Earth and a year on it is only 37 Earth days instead of 365. But astronomers do not think these are big differences and some of them think Gliese 581g will be a new Earth. However, Gliese 581g is twenty light-years from Earth – a distance of 18 trillion km.

What is the main idea of the passage?