阅读下面短文，掌握其大意，从每题所给的A、B、C、D四个选项中，选出最佳选项，并在答题卡上讲该项涂黑。
A Race Against Death
It was a cold January in 1925 in North Alaska. The town was cut off from the rest of the world due to heavy snow.
On the 20th of that month, Dr.Welch 36 a Sick boy, Billy, and knew he had diphtheria, a deadly infectious(传染的)disease mainly affecting children. The children of Nome would be 37 if it struck the town. Dr.Welch needed medicine as soon as possible to stop other kids from getting sick. 38 , the closest supply was over 1,000 miles away, in Anchorage.
How could the medicine get to Nome? The town`s 39 was already full of ice, so it couldn`t come by ship. Cars and horses couldn`t travel on the 40 roads. Jet airplanes and big trucks didn`t exist yet.
41 January 26, Billy and three other children had died. Twemty more were 42 . Nome`s town officials came up with a(n) 43 . They would have the medicine sent by 44 from Anchorage to Nenana. From there, dogeled(狗拉雪橇)drivers—known as “mushers”—would 45 it to Nome in a relay(接力).
The race began on January 27. The first musher, Shannon, picked up the medicine from the train at Nenana and rode all night. 46 he handed the medicine to the next musher, Shannon`s face was black from the extreme cold.
On January 31， a musher named Seppala had to 47 a frozen body of water called Norton Sound .It was the most 48 part of the journey. Norton Sound was covered with ice,which could sometimes break up without warning.If that happened,Seppala might fall into the icy water below.He would 49 ,and so would the sick children of Nome.But Seppala made it across.
A huge snowstorm hit on February 1.Amusher named Kaasen had to brave this storm.At one point,huge piles of sonw blocked his 50 .He had to leave the trail (雪橇痕迹)to get around them.Conditions were so bad that it was impossible for him to 51 the trail again. The only hope was Balto,Kaasen’s lead dog, Balto put his nose to the ground, 5 2 to find the smell of other dogs that had traveled on the trail.If Balto failed,it would mean disaster for Nome.The minutes passed by.Suddenly, Balto began to 53 .He had foung the trail
At 5:30 am on February 2, Kaasen and his dog 54 in Nome. Within minutes,Dr.Welch had the medicine.He quickly gave it to the sick children.All of them recoverd.
Nome had been 55 .
46（）
A.Though
B.Since
C.When
D.If
