实数a分别取什么值时，复数是（1）实数；（2）虚数；（3）纯虚数。

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  A、will paint

  B、had painted

  C、is being painted

  D、has been

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• 已知平面向量，若存在不同时为零的实数k和t，使。（1）试求函数关系式k=f（t）；（2）求使f（t）>0的t的取值范围。

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• Passage1 In many of the developing countries in Africaand Asia, the population is growing fast. The reason for this is simple: Womenin these countries have a high birth rate - from 3.0 to 7.0 children per woman.The majority of these women are poor, without the food or resources to care fortheir families. Why do they have so many children? Why don't they limit thesize of their families? The answer may be that they often have no choice. Thereare several reasons for this. Onereason is economiIn atraditional agricultural economy, large families are helpful. Having morechildren means having more workers in the fields and someone to take care ofthe parents in old age. In an industrial economy, the situation is different.Many children, do not help a family; instead, they are an expense. Thus,industrialization has generally brought down the birth rate. This was the casein Italy, which was industrialized quite recently and rapidly. In the earlypart of the twentieth century, Italy was a poor, largely agricultural countrywith a high birth rate. After World WarⅡ, Italy's economy was rapidly modernized and industrializeBy theend of the century, the birth rate had dropped to 1. 3 children per woman, theworld's lowest.However,the economy is not the only important factor that influences birth rate. SaudiArabia, for example, does not have an agriculture-based economy, and it has oneof the highest per capita incomes in the worlNevertheless,it also has a very high birth rate. Mexico and Indonesia, on the other hand,are poor countries, with largely agricultural economies, but they have recentlyreduced their population growth. Clearly,other factors are involveThemost important of these is the condition of women. A high birth rate almostalways goes together with lack of education and low status for women. Thiswould explain the high birth rate of Saudi Arabia. There, the traditionalculture gives women little education or independence and few possibilitiesoutside the home. On the other hand, the improved condition of women in Mexico,Thailand, and Indonesia explains the decline in birth rates in these countries.Their governments have taken measures to provide more education andopportunities for women. Anotherkey factor in the birth rate is birth control. Women may want to limit theirfamilies but have no way to do so. In countries where governments have madebirth control easily available and inexpensive, birth rates have gone down.This is the case in Singapore, Sri Lanka, and India, as well as in Indonesia,Thailand, Mexico, and Brazil. In these countries, women have also been providedwith health care and help in planning their families. Thesetrends show that an effective program to reduce population growth does not haveto depend on better economic conditions.3 It can be effective if it aims tohelp women and meet their needs. Only then, in fact, does it have any realchance of success.       (495 words) When countries become industrialized, _______.

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