临床上最常见和最具有代表性的急性肾衰是 A．重症肾小球肾炎 B．重症肾盂肾炎 C．重

Directions: For each blank in the following passage there are four words or phrases marked A, B, C and D. Fill in each blank with the word or phrase that best fits the context.

The central problem of economics is to satisfy the people's and nation's wants.

The problem we faced with is that our resources, here identified as money are __50__. The only way we can solve the problem is to make choices. After looking at our resources, we must examine our list of __51__ and identify the things we need immediately, those we can postpone, and __52__ we cannot afford. As individuals, we face the central problem involved in economics---deciding how to allocate(分配) our limited resources to provide __53__ with greatest satisfaction of our wants.

Nations face the same problem. As a country's population __54__, the need for more goods and services grows correspondingly. Resources necessary to production may increase, but there are __55__ enough resources to satisfy the total desires of a nation. Whether the budget meeting is taking place in the family living room, in the conference room of the corporation __56__ of directors, or in the chamber of the House of Representatives in Washington, the basic problem still exists. We need to find __57__ of allocating（分配） limited resources in order to satisfy unlimited wants.

A short time ago, economists divided goods into two categories, free and economic. The former, like air and water, were in __58__ abundance(丰富) that economists had___59____ them. After all, economics is the __60__ of scarcity and what to do about it. Today many of these "free goods" are __61_ very expensive to use. Population has made clean air and water expensive for producers extra cost, and __62__ taxpayers who pay for the government's involvement in cleaning the environment.

In the 1990s, almost all goods are __63__. Only by effort and money can they be obtained .

Meeting needs of people and the demands from resource available __64__ the basic activity of production. In trying to meet unlimited wants from limited economic goods, production leads to new problems in economics.

50.A. limited    B. unlimited     C. scarcity       D. abundant

51.A. want       B. problem      C. wants          D. resources

52.A. those      B. some C. others         D. many

53.A. them       B. themselves C. ourselves    D. ours

54.A. expand   B. extends        C. grows          D. increase

55.A. always    B. sometimes          C. often D. never

56.A. management         B. function      C. board           D. group

57.A. people    B. economists C. way     D. methods

58.A. so   B. great   C. such    D. such an

59.A. much concern forB. no concern with     C. no concern for     D. much concern in

60.A. form        B. study C. means         D. source

61.A. possibly          B. in practice C. in fact          D. practically

62.A. from       B. at        C. for       D. with

63.A. plentiful          B. scarce         C. abundant    D. in full supply

64.A. are led to       B. leading to   C. lead to         D. leads to

HTK-391型轴温探测系统判断列车全部通过的条件是（）。

NEG指令是一个（）操作数指令。

A.单

B.双

C.无

D.任意多个

烈性噬菌体和温和噬菌体的区别是什么

禽流感是由禽类流感病毒引起的，是一类对家禽和人类有直接或间接危害的传染病，下列叙述中属于体液免疫的是（）

①注射禽流感病毒疫苗，使机体产生抗体，与入侵的禽流感病毒结合，抑制病毒的活性

②在人体内使禽流感病毒失去感染人体细胞的能力

③效应T细胞产生淋巴因子发挥免疫效应

④形成沉淀被吞噬细胞吞噬消化

⑤效应T细胞与靶细胞密切接触，导致靶细胞裂解，释放禽流感病毒

⑥将患病的家禽深埋处理

A.①②③

B.②⑤⑥

C.①③④

D.①②④