阅读下面材料,在空白处填入适当的内容(1个单词)或括号内单词的正确形式。
Every winter in Alaska a race is held. But this is no ordinary race. Teams of dogs pull sleds(雪橇)along the snow and ice, ____ (carry) up to 500 kg of supplies. A single driver is in charge of each team, and stands on the sled. This race
___ (know) as Iditarod runs from the town of Anchorage to the village of Nome, a journey of more than l,800 kilometers. It usually takes the teams about ten days to complete the course.
The Iditarod is usually run in _____ (extreme) difficult weather conditions.Daytime
_____ (temperature) range from zero to minus 40 degrees. Visibility(能见度)is often very poor, so drivers never allow
_____ (them) to become separated from their team of dogs.
____ , the drivers depend almost entirely on the dogs for their survival.
The origin of the race ______ (go) back many years to a time
____ some medicine needed to be taken from Anchorage to Nome, a very remote village. Because of severe weather, the only way to send the medicine
____ (be) to use dogs. Happily, the medicine was delivered just
_____ time to save lives. To celebrate the heroic journey, Alaskans developed the Iditarod.