[简答题]功率因数低的原因是什么？

案例一
[背景材料]
某大型剧院拟进行维修改造，某装饰，装修工程在公开招标投标过程中获得了该维修改造任务，合同工期为5个月合同价格为1800万元。
1．抹灰工程基层处理的施工过程部分记录如下：
(1)在抹灰前对基层表面做了清除；
(2)室内墙面、柱面和门窗洞口的阳角做法符合设计要求。
2．工程师对抹灰工程施工质量控制的要点确定如下：
(1)抹灰用的石灰膏的熟化期不应小于3d；
(2)当抹灰总厚度大于或等于15mm时，应采取加强措施；
(3)有排水要求的部位应做滴水线(槽)；
(4)一般抹灰的石灰砂浆不得抹在水泥砂浆层上；
(5)一般抹灰和装饰抹灰工程的表面质量应符合有关规定。
[问题]

The professor talked to American and Brazilian students about lateness in both an informal and a formal situation: lunch with a friend and in a university class, respectively. He gave them an example and asked them how they would (1) if they had a lunch appointment with a friend, the average American student (2) lateness as 19 minutes after the (3) time. On the other hand, the average Brazilian student felt the friend was late after 33 minutes.
In an American university., students are expected to arrive at the appointed (4) Classes not only begin, but also end at the (5) time in the United States. In the Brazilian class, only a few students left the class at noon; many (6) past 12:30 to discuss questions. (7) arriving late may not be very important in Brazil, (8) is staying late. The (9) for these differences is complicated. People from Brazilian and North American (10) have different feeling about late
A. either
B. neither
C. but
D. also

In 99 cases out of a 100, insomnia (失眠) is caused by a disturbance of the natural sleep rhythm. The reasons why the rhythm has been disturbed are many; they can range from drugs to alcohol to mental illness to health problems to unresolved stress to bad sleep habits. A sudden change in lifestyle or climate can do it, or a change in a job or an emotional relationship.
Certainly the body must have enough sleep. Tests of sleep-deprived people have proved that lack of sleep can cause fairly rapid physical and mental deterioration (退化). On the other hand, the body doesn’t need too much sleep. So if you’re sleeping in front of the TV, you might find it difficult to sleep soundly at night. Similarly, if you’re holidaying in Spain and spending your days sleeping on the beach, chances are that you’ll be wide awake at bedtime.
One interesting phenomenon regarding insomnia is that of summer insomnia. Some people have difficulty sleeping during
A. a sudden change in lifestyle
B. good bodily condition
C. the habit of falling asleep in front of the television
D. a quick drop in both physical and mental condition