关于合同的生效，以下说法错误的是( )。A．依法成立的合同，自成立时生效 B．附生

Performing better under pressure

What is the most stressful thing in school? It is probably exams．小题1:．       But some students succeed under pressure，while others struggle．So，why do some students perform better under stress?

It all comes down to dopamine （多巴胺）． Dopamine is a chemical in our body that sends signals （信号） in the brain．It has many important roles：affecting memory，attention and how we learn．小题2:．       

Our brains control dopamine in two ways．It either takes out dopamine quickly，or gradually．Exam success can be linked to how fast dopamine goes back to a balance，according to new research from the University of Missouri，reported Yahoo．

小题3:．       If you become stressed，your brain will start to overload （起负荷） on dopamine．It is like a cup overflowing with water．The quicker you are able to go back to a balance of dopamine，the quicker you can concentrate．小题4:．      

Researchers found that，during a test，people who slowly got back to a balance of dopamine scored 8 percent lower． That’s me difference between a good mark and a bad mark．

But don't fear，there is good news for every student．小题5:．    So，it turns out that practice really makes perfect．

根据短文内容，从下面五个选项中选出能填入文中空缺处的最佳选项，使短文意思通顺、内容完整，并在答题卡上将该项涂黑。

A．This will help you perform better on a test．

B．Exams can put us under a lot of pressure．

C．The study also found that the more practice you get，the less stressed you’ll be．

D．What happens when we take an exam?E．Our brains work best when there is a balance of dopamine—not too much or too little．

家用血糖分析仪选购和使用的注意事项是（）

A.更换新批号试条时先进行校准

B.血糖试条必须和其适配的血糖仪一起使用

C.应在血糖试条有效期内使用

D.定期对仪器进行校正

E.按规定温度保存血糖试条

如图所示电路，电表均为理想电表，闭合开关后电压表的示数为U，电流表的示数为I，电源的电动势为E且保持不变、内阻不可忽略．当滑动变阻器的滑片向左移动时（　　）

A．U不变，I变小

B．R₁消耗的功率不变

C．R₂两端的电压变大

D．电源的效率变大

男性，28岁，腰背痛10年，开始时腰骶部疼痛向双臀部放射。曾在县医院诊断为腰椎间盘突出症。后腰骶部痛减轻，背痛加重，并逐渐出现驼背畸形，双髋活动部分受限，上三楼后气喘、呼吸困难。查体：脊柱活动明显受限，肺活量明显减少，Thomas征阳性，床边试验阳性，血液检查RF（-），HLA-B27（+），AS0200U，ESR54mm/h。初步诊断应首先考虑（）。

A.类风湿性关节炎

B.DISH病

C.强直性脊柱炎

D.脊柱结核

E.肥大性脊柱炎

The study of meaning in language is known as semantics.