Прочитайте текст с пропусками, обозначенными номерами. Эти номера соответствуют заданиям А21-А28, в которых представлены возможные варианты ответов. Обведите номер выбранного вами варианта ответа. TEST  18  ( part 3)

Is there intelligent life elsewhere in the universe? One quite valid response to that question is: we just don't know and we haven't seen any proof that there is so A21………………. . (Some people's claims that they have seen UFOs certainly do not count as proof. They are not even evidence.)

However, scientists are becoming increasingly A22 ………………. that the Earth is not the only source of life in the universe.

There are two main reasons for this. The first is that the more scientists learn about how life started here on Earth, the more they realise how easily those conditions could be recreated somewhere else.

The second reason is A23 ………………. to the first. A24………………. it's not that difficult to create the right conditions for life to form, the universe is so big that the A25………………. are if it can happen somewhere else, it will.

None of that is to A26 ………………., however, that we'll be communicating with aliens any time soon. Firstly, if there is life on other planets, it may not be intelligent in the way that humans are. There are billions of different life forms here on Earth, but it's only humans who have been able to leave the planet. Secondly, A27………………. if there was an intelligent life form on another planet, it may have evolved and become extinct billions of years before the Earth even formed. Or, it may not come into existence until billions of years in the future. Thirdly, one of the main reasons why there might be life elsewhere - the sheer size of the universe - is also a reason why we will probably never A28 ………………. to see it. It takes so long to travel even short distances in space – the journey from Earth to our close neighbour Mars takes several months - the odds of two intelligent life forms from different planets being in the same place at the same time are incredibly small.