与病例对照研究比较，前瞻性队列研究最明显的优点是 A．用于探讨疾病的发病因素 B．疾

小老树是指树龄虽小，但长势已经显著衰弱的树。具体表现为树体小，短枝多，枝细弱，叶片小，落叶早，果实小等。读右图完成19～20题。

小题1:下列与图中小老树主要分布相符合的是

A．位于干旱半干旱交界处

B．位于温带落叶阔叶林与亚热带常绿阔叶林过渡带上

C．位于农业与畜牧业过渡区

D．位于暖温带与中温带的交界处小题2:影响小老树分布的主要因素是

A．土壤贫瘠

B．气候不适

C．地形崎岖

D．河流过少

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  .

50（）

A.memory

B.exit

C.way

D.destination

自我胎动计数，哪项为异常

A．＞3次/小时

B．＞5次/小时

C．＜10次/12小时

D．＞20次/12小时

E．＞30次/12小时

V带产生的摩擦力是平带的（），所以能传递较大功率。

A.2倍

B.2.5倍

C.3倍

D.4倍

智力落后儿童的测查与鉴别，要由（）进行。

A.教师

B.幼儿园或学校领导

C.专业人员

D.所有这些人员