引起SAS最常见的危险因素是（）。 A.年龄 B.肥胖 C.性别 D.局部解剖异常

计算：a•a²=______．

选择正确的选项完成对话。

A What are you going to do this year?

B Linda, what are you going to be when you grow up?

C That sounds great

D What kind of job do you want?

E Why are you going to get a part time job?

Peter:  1._______

Linda: I'm going to be a teacher when I grow up.

Peter: 2._______

Linda: I'm going to work harder in school this year. And I'm going to get a part-

    time job.

Peter: 3._______

Linda:  I want to put some money in the bank.  I'll need money for college.

Peter: 4._______

Linda: I want to work with computer.

Peter: 5._______

在PCR反应中，经过n次循环，理论上DNA链的数目扩增了多少倍？（）

A.n倍

B.2n倍

C.4n倍

D.2ⁿ倍

E.n²倍

平行承发包模式的缺点有( )。

A．合同数量多，管理难度大
B．建设周期长
C．不利于业主选择承建单位
D．不利于建设工程的组织管理

有关铁代谢的检查中，较灵敏地反映体内贮铁情况，在缺铁的铁减少期即有改变的指标是

A．血清铁
B．血清铁蛋白
C．总铁结合力
D．骨髓可染铁
E．红细胞游离原卟啉