工程中常用的低压电气设备有（）。A．桥架 B．低压断路器 C．刀开关 D．接触器

“每个人都力图为他的资本找到最有利的用途。”他受着一只看不见的手的指导，去尽力达到一个并非他本本意要选到的目的。他迫求自己的利益往往使他能比在真正出于本意的情况下，更有效地促进社会利益。”斯密的上述观点

①认为追求个人利益是人们从事经济活动的唯一动力

②认为个人追求私利的行为能够促进社会利益的实现

③主张通过市场机制作用下的自由竞争实现富国裕民

④看到了社会分工可以提高劳动生产率促进财富增长

A．①②③

B．①②④

C．①③④

D．②③④

遗精的病因主要是（）

A.劳心太过

B.饮食不节

C.大惊卒恐

D.欲念不遂

E.恣情纵欲

Organic foods are produced according to certain production standards, meaning they are grown without the use of conventional pesticides, or chemical fertilizers and that they were processed without food additives. Livestock are raised without the routine use of antibiotics（抗生素）or growth hormones. In most countries, organic produce must not be genetically modified. They may also be required to be produced using energy-saving technologies and packaged using recyclable materials when possible.

Early consumers interested in organic food would look for non-chemically treated, fresh or minimally processed food.

They mostly had to buy directly from growers: “Know your farmer, know your food” was the motto. Personal definitions of what constituted ( 组成)“organic” were developed through first-hand experience: by talking to farmers, seeing farm conditions, and farming activities. Historically, organic farms were relatively small family-run farms — which is why organic food was once only available in small stores or farmers’ markets.

However, since the early 1990s organic food has had growth rates of around 20% a year. As of April 2008, organic food accounts for 1 - 2% of food sales worldwide. Currently organic food production is legally regulated. Many countries require producers to obtain organic certification in order to market food as organic.

Several studies have attempted to examine and compare conventional and organic systems of farming. The general consensus（共同看法）is that, in the short term, organic farming is less damaging for the following reasons:

● Organic farms do not release synthetic pesticides (合成农药) into the environment — some of which have the potential to harm soil, water and local wildlife.

● Organic farms are better than conventional farms at keeping diverse ecosystems, i.e., populations of plants and insects, as well as animals.        

● Organic farms are more energy efficient and produce less waste.

Another report published in March 2008 by The Organic Center claims that organic food is on average 25% more nutritious than conventional food.     

However, many critics believe that the increased land needed to farm organic food could potentially destroy the rainforests and wipe out many ecosystems. And organic products cost 10 to 40% more than similar conventionally produced products. Processed organic foods in supermarkets are 65% more expensive.

1. Early consumers knew what food was “organic” by _______.

A. firsthand experience                                     B. the “certified organic” label tag

C. its packaging                                                      D. examining its organic certification

2. We can infer that _______.

A. in America, organic food can only be bought in small stores or farmers’ markets

B. organic food is also available in large supermarkets at present

C. organic food is produced by large-scale farms

D. organic food is often beautifully packaged

3. According to the passage, organic food is considered as _______.     

A. junk food              B. delicious snacks               C. green food      D. conventional food

4. What is the main idea of the last paragraph?

A. The benefits of organic food.                               B. The cost of organic food.

C. The disadvantages of organic food.                   D. Organic food and conventional food.

5. Which of the following statements does NOT support the view that organic farming is more environment-friendly?

A. Organic food is generally thought to be more nutritious.

B. Organic farms are more energy efficient and produce less waste.

C. Organic farms are better than conventional farms at maintaining varieties of plants, insects and animals.

D. Organic farms do not release synthetic pesticides into the environment.

带压开孔作业时应根据管道材质，输送介质、运行参数、管道（）选择带压开孔设备。

A、直径

B、内径

C、外径

D、口径

免疫球蛋白经酶水解后，可与两个相应抗原结合的片段是（）

A.Fab

B.F（ab′）

C.Fc

D.PFc′

E.Fd