服务程序是一类辅助性程序，它提供各种软件运行时所需的服务。下列哪一个属于服务程序 A

设3阶实对称矩阵A的特征值是1，2，3；矩阵A的属于特征值1，2的特征向量分别是α₁=(-1，-1，1)^T，α₂=(1，-2，-1)^T．
(1) 求A的属于特征值3的特征向量；
(2) 求矩阵A．

除去镁粉中混有的少量铝粉, 可选用的试剂是

A．盐酸

B．NaOH溶液

C．硝酸

D．食盐水

阅读理解。

     Running, as most of you already know, is a sport that all sorts of people love. Running a marathon is also

something that many long-distance runners have as a goal. Now if you decide you want to train for a marathon,

how do you go about getting yourself into excellent shape for the race of your life? 

     Most marathon training schedules last around 20 weeks and are designed for runners who can run 4-5 days

per week. The secret of a successful training schedule lies in avoiding injury that can happen through pushing

yourself too fast or too hard. So, the idea is to increase your mileage gradually from, let's say,20 miles per week

up to runs of 50 miles per week at some point before the actual marathon. Alternate (交替) hard days with easy

days: an easy day could be a day off altogether or something else like a three-mile run which, although it might

not seem to be really worth the effort to some of you, actually is a joy to do.

     Be careful how you warm up and slow down, because these are the times when injuries could happen. When

you set off for a run, take the first mile slowly and when you break into a sweat, stop and do some stretching

exercises for a couple of minutes. Always take the last mile slowly too-if you stop suddenly after a hard run,

then those of you who might have heart attacks are putting yourselves at greater risk at the point. One word of

warning: don't start a training schedule without some guidance from a properly qualified trainer. He or she will

be able to tell you what you're doing right or wrong! Remember that under normal circumstances, health

benefits from regular running are an increased sense of energy and well being, together with fitness.

1. In the second paragraph, the writer says that _____. [ ]

A. it's not worth doing a three-mile run

B. there should be some easy days rather than hard days

C. the training period should last for three weeks

D. a short run can be a pleasant experience

2. The most dangerous times are when you are _____. [ ]

A. starting and stopping

B. building up speed

C. running hard

D. sweating a lot

3. This article might be written for _____. [ ]

A. people interested in taking up running

B. young athletes

C. people already involved in running

D. athletics trainers

4. If you run on a regular basis, you will _____.[ ]

A. avoid having heart attacks

B. be able to win a marathon

C. feel better and more energetic

D. become a faster runner

对于高土壤电阻率地区的接地网，在接地阻抗难以满足要求时，应采用完善的（）及隔离措施，防止人身及设备事故，方可投入运行。

下列不符合缺铁性贫血的检验是

A．血清铁降低
B．血清总铁结合力降低
C．平均红细胞血红蛋白浓度降低
D．平均红细胞体积降低
E．血清铁蛋白降低