Near the North Pole there are only two seasons: winter and summer. The winter Nights are long. For more than two months you can't see sun, ever at noon. The summer days are long.For more than two months the never sets and there is no night at all. The weather is cold all the year round. Even summer the temperatures below 0°C. So people there make their clothing with the fur of animals.

    In the cold climate, plants cannot grow. So people have to build their houses with fur, earth, shone or snow. When they go out hunting, they live in the tents of the fur. When they move, they take their tents with them. Sometimes, they build houses of snow. Now don't think that these houses must be cold, it is very warm and safe.

    The life near the North Polo is very interesting.

果蝇的长翅（V）对残翅（v）为显性，纯合的长翅幼虫在25℃条件下培育成的成体果蝇为长翅，但在37℃条件下培育成的成体果蝇为残翅．下列叙述正确的是（　　）