串联管路的特点有哪些？

阅读理解。

For most students, the time of exams is very stressful and difficult. Some students find the exam time is so bad that they become ill, because they are afraid of failing, and they are afraid of letting their parents and families down. If exams are really making you ill or worried, don't hide your feelings. Talk to someone about it. If he or she doesn't help you, ask someone else.      Here are some top tips given by educational psychologists (教育心理学家):      (1) Ask a teacher about how to revise and about exam skills- how to work when you are in an exam.      (2) Take a short rest during your time of work and revision. If your mind is tired, it will not remember well.          (3) Revise at the time when you know you will work at your best.      (4) Get enough sleep, and eat healthy food.      (5) If you feel bad, talk to someone about your worries. But don't be too relaxed! Some stress over exams makes you work hard for them.      (6) If it upsets you to talk to your friends about an exam when it is finished, don't do it! In fact, don't even think about the exam you have finished. What is done has been done. You cannot change what you have written!          (7) If you are studying in the evening, don't go straight to bed afterwards. Your mind will still be "going round and round"- thinking too much. So something else, maybe walk or get exercise. Choose something that will relax you, and make you think of other things.

Problems Suggestions Don't know how to work for an exam. Ask a teacher about 1_______. Feel tired. 2_______. Feel bad or worried. It's necessary of you to 3_______. It upsets you to talk to your friends about   an exam when it is finished. Don't 4_______. when it is finished You can't fall asleep after studying in the evening. Don't 5_______. Do something else.

下表是重庆市近年来的城乡居民家庭恩格尔系数情况(单位:%),从表中可知近年来该市

年份	2005年	2006年	2007年	2008年	2011年	2012年
城镇居民家庭恩格尔系数	37.7	36.1	35.7	37.1	36.3	35.9
农村居民家庭恩格尔系数	47.2	46.6	44.5	46.5	40.4	40.1

①城乡居民收入不断增加　                  

②城乡居民家庭食品支出总额整体上呈现下降趋势　

③城乡居民的消费层次、消费质量不断提高　  

④农村居民消费水平低于城市居民消费水平

A．①②  B. ③④     C. ①③     D. ②④

高血压急症时常首选（）

A．硝普钠

B．低分子肝素

C．硝酸甘油

D．尼卡地平

E．链激酶

同样质量的水和原油汽化后，水蒸汽的体积要比油蒸气的体积（）。

A、相等

B、小

C、大得多

D、小得多

在IEEE 802系统协议中描述逻辑链路控制子层(LLC) 的功能、特性和协议的是 _______。

A．IEEE 802.5

B．IEEE 802.4

C．IEEE802.2

D．IEEE 802.3