شرکت در آزمون آنلاین زبان انگلیسی 1 - زبان انگلیسی 1 | آزمون شماره 14283

So far we haven’t been able to find much about this metal, but we are still ......... on it.

Most of the governments throughout the world express their concern about the ......... in the rate of population growth ageing over 65.

Why don’t birds get lost on their long migratory flights? Scientists have puzzled over this question for many years. Now they’re beginning to fill in the blanks.

Not long ago, experiments showed that birds rely on the sun to guide them during daylight hours. But what about birds that fly mainly by night? Tests with artificial stars have proved conclusively that certain night-flying birds are able to follow the stars in their long- distance flights.

One such bird, a warbler, had spent its lifetime in a cage and had never flown under a natural sky. Yet it showed an inborn ability to use the stars for guidance. The bird’s cage was placed under an artificial star-filled sky at migration time. The bird tried to fly in the same direction as that taken by his outdoor cousins. Any change in the position of the make-­believe stars caused a change in the direction of flight.

The reason why birds don’t get lost on migratory flights … .

The old man down the street always…….. to himself. I just realized I don’t even know his name.

That student is very smart, and always gets lots of … from the teachers at school.