下列说法正确的是 [ ] A.原电池是把电能转化为化学能的装置 B.原电池中电子

题型:不定项选择题

问题:

下列说法正确的是 [ ]

A.原电池是把电能转化为化学能的装置

B.原电池中电子流出的一极是正极,发生氧化反应

C.原电池的电极发生的反应均为氧化还原反应

D.形成原电池后,原电池中的阳离子向正极移动

考点:原电池原理
题型:不定项选择题

支气管扩张合并咯血时治疗一般不主张应用()

A.抗生素

B.止血药

C.镇咳药

D.支气管舒张药

E.镇静药

题型:不定项选择题

下列说法正确的是

A.同温同压下,相同数目的分子必具有相同的体积

B.等质量的O2和H2的物质的量之比为16∶1

C.不同的气体若体积不等,则它们所含的分子数一定不等

D.同温同体积下,两种气体的物质的量之比等于压强之比

题型:不定项选择题


The central problem of economics is to satisfy the people’s and nation’s wants. The problem we are faced with is that our (1) , here identified as money, are (2) . The only way we can resolve our (3) is to make choices. After looking at our resources, we must examine our list of (4) and identify the things we need (5) , those we can postpone, and (6) we cannot afford. As individuals, we face the central problem involved in economics — deciding just how to allocate our limited resources to provide ourselves with the greatest (7) of our wants.
Nations face the same problem. As a country’s population (8) , the need for more goods and services grows (9) . Resources necessary to production may increase, but there are (10) enough resources to satisfy the total desires of a (11) . Whether the budget meeting is taking place in the family living-room, in the conference room of the corporation (12) of directors, or in the chamber of the House of Representatives in Washington, the basic problem still exists. We need to find (13) of allocating 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 (14) abundance that economists had no concern about (15) of scarcity and what to do about it. Today many of these "free goods" are in (16) very expensive to use. Pollution has made clean air and water expensive for producers who have to filter their waste products, for consumers who ultimately pay for the producers’ extra costs, and (17) tax-payers who pay for the government’s involvement in cleaning the environment.
In the 1990s, almost all goods are (18) . Only by effort and money can they be (19) in the form people wish.
Meeting the needs of people and the demands from resources available leads to the basic activity of production. In trying to (20) unlimited wants from limited economic goods, production leads to new problems in economics.

题型:不定项选择题

怎样合理使用棉粕?

题型:不定项选择题

如用符号JDF和JD分别表示酚酞碱度和全碱度,若2JDF<JD,则可判断该水样中()。

A.只含有OH碱性离子

B.只含有CO32-碱性离子

C.只含有HCO3碱性离子

D.OH和CO32-共存

E.CO32-和HCO3共存

更多题库