凡是在矿井开拓、采掘过程中，以不同形式进入矿井的水，统称为矿井水。

民间流传用硝土和草木灰作原料来制取硝酸钾．硝土中含有硝酸钙和氯化钠物质，草木灰的主要成分是碳酸钾．制作的工艺流程主要如图所示：

（1）③⑤⑦均为操作X，该操作是      ；

（2）结合图，分析工艺流程中用加热蒸发方法得到氯化钠晶体，而用冷却结晶法得到硝酸钾晶体的原因                                                ．

（3）写出生成白色沉淀B的化学方程式：                                 ．

（4）用含硝酸钙为50%的硝土40kg与草木灰混合，按上述工艺流程，理论上能制取硝酸钾的质量是         kg（保留1位小数）．

（5）溶液D可以重复使用的原因是                          ．

Questions 24-30

30 Which is NOT a part of the surveys

A．The ratios of students to academics.

B．The proportion of overseas students and staff at each university.

C．The number of times each university’s academics quote others’ researc

依据《外商投资企业和外国企业所得税法》的有关规定，外国企业向我国境内企业单独转让邮电、通讯等软件，或者随同销售邮电、通讯等软件，转让这些设备使用的软件所取得的软件使用费，可按（）。

A．30%的税率征收所得税

B．20%的税率征收所得税

C．10%的税率征收所得税

D．免征所得税

Increasingly, historians are blaming diseases imported from the Old World for the great disparity between the native population of America in 1492--new estimates of which jump as high as 100 million, or approximately one-sixth of the human race at that time--and the few million full-blooded Native Americans alive at the end of the nineteenth century. There is no doubt that chronic disease was an important factor in the sharp decline, and it is highly probable that the greatest killer was epidemic disease, especially as manifested in virgin-soil epidemics.

Virgin-soil epidemics are those in which the populations at risk have had no previous contact with the diseases that strike them and are therefore immunologically almost defenseless. That virgin-soil epidemics were important in American history is ply indicated by evidence that a number of dangerous maladies--smallpox, measles, malaria, yellow fever, and undoubtedly several more--were unknown in the pre-Columbian New World. The effects of their sudden introduction are demonstrated in the early chronicles of America, which contain reports of horrible epidemics and steep population declines, confirmed in many cases by quantitative analyzes of Spanish tribute records and other sources. The evidence provided by the documents of British and French colonies is not as definitive because the conquerors of those areas did not establish permanent settlements and began to keep continuous records until the seventeenth century, by which time the worst epidemics had probably already taken place. Furthermore, the British tended to drive the native populations away, rather than to enslave them as the Spaniards did; so that the epidemics of British America occurred beyond the range of colonists’ direct observation.

Even so, the surviving records of North America do contain references to deadly epidemics among the native population. In 1616--1619 an epidemic, possibly of pneumonic plague, swept coastal New England, killing as many as nine out of ten. During the 1630’s smallpox, the disease most fatal to the Native American people, eliminated half the population of the Huron and Iroquois confederations. In the 1820’s fever ruined the people of the Columbia River area, killing eight out of ten of them.

Unfortunately, the documentation of these and other epidemics is slight and frequently unreliable, and it is necessary to supplement what little we de know with evidence from recent epidemics among Native Americans. For example, in 1952 an outbreak of measles among the Native American inhabitants of Ungava Bay, Quebec, affected 99 percent of the population and killed 7 percent, even though some had the benefit of modern medicine. Cases such as this demonstrate that even diseases that are not normally fatal can have destroying consequences when they strike an immunologically defenseless community.

Notes: disparity 差距。 virgin-soil处女地。 malady 疾病 chronicle 编年史。 tribute 贡品。 pneumonic plague肺鼠疫。confederation 同盟。 smallpox 天花。measles 麻疹。

It can be inferred from the text about the Native American inhabitants of Ungava Bay that they（）

A. could scarcely ward off the fatal attack by the 1952 epidemic

B. were immunologically defenseless against measles

C. were the last native people to be struck by a virgin-soil epidemic

D. did not come into frequent contact with White Americans until the 20th century

保险代理从业人员从事人寿保险代理业务时______。

A．可以同时接受两家或两家以上人寿保险公司的委托
B．可以同时接受多家人寿保险公司的委托
C．只能接受一家人寿保险公司的委托
D．只能接受两家人寿保险公司的委托