伺服机制系指（）A.干扰信号对控制装置的直接作用 B.反馈信息影响控制装置之前的活动

根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。选项中有多余选项。

The Dark Age of Greece

小题1:Among early civilizations, we call the low points "dark ages", because civilizations often dropped to such a low level that it is hard to get an accurate picture of their history during these periods. During a dark age, a civilization may not have produced monuments, statue, or other objects which we use to learn about early civilizations.

One' of the most important dark ages was the dark age of Greece,which lasted from about 1100 BC to 900 BC. Prior to-that-time,Greece had a highly advanced society called the Mycenaean civilization. The Mycenaeans were a trading civilization小题2:In fact, the Mycenaean civilization was so important that when it collapsed in the 12th centuryBC,most other civilizations in the region collapsed as well.The next 200 years are like a blank page to  historians and we know very little about this period.小题3:The collapse of the Mycenaeans brought an end to writing in the area, and thus an end to the written records historians rely on.

The little that we know about this period has been learned from archaeology. It seems that civilization became much less advanced. The pottery from this period is much simpler and less artistic. This suggests that there was lack of wealthy people to buy higher quality products. 小题4:   This would suggest a large decrease in population, possibly due to a widespread lack of food and consequent starvation.

Sometime around 800 BC, the Greeks began to emerge from this dark age, most probably due to the influence of other civilizations. They had lost their early writing system, but began to use the writing system of the Phoenicians at this time.小题5:Over the next 300 years, their civilization continued to rise, and their dark age was forgotten.

A．Many civilizations undergo a series of high points and low points during their history.

B．Many early civilizations underwent dark ages, but Greece never recovered from its dark age.

C．They began constructing larger cities and trading with their neighbors again.

D．Another interesting point is that most of the large cities of earlier time periods appear to have been abandoned in favor of much smaller settlements.E.Many pieces of evidence suggest that there was a huge increase in population during the dark age of Greece.

F.and they did much to spread their culture across the eastern Mediterranean.

G.One major reason for this is that writing basically stopped.

下列有关烷烃的叙述中，正确的是[ ]

A．烷烃能与氯水在光照和适当的温度下发生取代反应

B．烷烃中除甲烷外，其他烷烃都能使酸性KMnO₄溶液褪色

C．碳原子数不相同的烷烃不一定互为同系物

D．等质量的烃完全燃烧时，甲烷消耗的氧气最多

老年性 * * 炎的治疗原则为（）、（）。

在比常规偏宽的跑道进近时，有可能出现的错觉是（）.

A.感觉自己的进场高度偏高；

B.感觉自己的进场高度偏低；

C.感觉飞机在带坡度飞行。

安全期避孕的描述正确的是（）

A、在排卵期进行避孕

B、在月经期避孕

C、在月经后5天避孕

D、在月经后7天避孕