若x=3，y=1是方程3x-ay=2的一个解，则a=（ ）。

下列可应用杠杆原理获得省力效果的拔伸法是（）

A.腰椎瞬间拔伸法

B.腰椎缓力拔伸法

C.坐位颈椎拔伸法

D.仰卧位颈椎拔伸法

作尿糖定量检查应加入的防腐剂是

A．95%酒精
B．浓盐酸
C．甲苯
D．稀盐酸
E．甲醛

胶带输送机打滑的原因是什么？

Believe it or not, optical illusion can cut highway crashes.

Japan is a case in point. It has reduced automobile crashes on some roads by nearly 75 percent using a simple optical illusion. But stripes, called chevrons, painted on the roads make drivers think that they are driving faster than they really are, and thus drivers slow down.

Now the American Automobile Association Foundation for Traffic Safety in Washington D.C. is planning to repeat Japan’s success. Starting next year, the foundation will paint chevrons and other patterns of stripes on selected roads around the country to test how well the patterns reduce highway crashes.

Excessive(too great) speed plays a major role in as much as one fifth of all fatal traffic accidents, according to the foundation. To help reduce those accidents, the foundation will conduct its tests in areas where speed-related hazards (danger) are the greatest curves, exit slopes, traffic circles, and bridges.

Some studies suggest that straight, horizontal bars painted across roads can initially cut the average speed of drivers in half. However, traffic often returns to full speed within months as drivers become used to seeing the painted bars.

Chevrons, scientists say, not only give drivers the impression that they are driving faster than they really are but also make a lane appear to be narrower. The result is a longer lasting reduction in highway speed and the number of traffic accidents.

The advantage of chevrons over straight, horizontal bars is that the former（）

A. can keep drivers awake

B. can cut road accidents in half

C. will look more attractive

D. will have a longer effect on drivers

关于抗微生物药物变态反应正确的叙述是（）

A.变态反应种类多，如过敏性休克、药物热、皮疹、血清病样反应、血管神经性水肿

B.引起过敏性休克最常见的抗微生物药物为青霉素，其次为链霉素

C.皮疹是最常见的变态反应，氨苄西林是最常出现皮疹的抗生素

D.药物热诊断较为困难，常有严重中毒症状，血中嗜酸性粒细胞减少

E.出现过敏性休克应及时转院治疗