[求助] feifei 117&122

117. A certain viral infection is widespread among children, and about 30 percent of children infected with the virus develop middle ear infections. Antibiotics, although effective in treating bacterial infections, have no effect on the virus. Yet when middle ear infections in children infected with the virus are treated with antibiotics, the ear often clear up.

Which one of the following most helps to explain the success of the treatments with antibiotics?

(A) Although some types of antibiotics fail to clear up certain infections, other types of antibiotics might provide effective treatment for those infections.

(B) Children infected with the virus are particularly susceptible to bacterial that infect the middle age.

(C) Many children who develop middle ear infections are not infected with the virus.

(D) Most viral infections are more difficult to treat than are most bacterial infections.

(E) Among children not infected with the virus, fewer than 30 percent develop middle ear infections.

122. Photovoltaic power plants produce electricity from sunlight. As a result of astonishing recent technological advances, the cost of producing electric power at photovoltaic power plants, allowing for both construction and operating costs, it one-tenth of what it was 20 years ago, whereas the corresponding cost for traditional plants, which burn fossil fuels, has increased. Thus, photovoltaic power plants offer a less expensive approach to meeting demand for electricity than do traditional power plants.

The conclusion of the argument is properly drawn it which one of the following is assumed?

(A) the cost of producing electric power at traditional plants has increased over the past 20 years.

(B) Twenty years ago, traditional power plants were producing 10 times more electric power than were photovoltaic plants.

(C) None of the recent technological advances in producing electric power at photovoltaic plants can be applied to producing power at traditional plants.

(D) Twenty years ago, the cost of producing electric power at photovoltaic plants was less than 10 times the cost of producing power at traditional plants.

(E) The cost of producing electric power at photovoltaic plants is expected to decrease further, while the cost of producing power at traditional plants is not expected to decrease.

answer: B, D

This question requires to be identified an assumption that would allow the argument’s conclusion to be properly drawn. As the argument is stated, there is a logical gap between the information given in the premises and the claim made in the conclusion:

Premise1: The cost of producing electric power at photovoltaic power plants is one-tenth of what it was 20 years ago.

Premise 2: The corresponding cost for traditional plants has increased.

Conclusion: Photovoltaic power plants offer a less expensive approach to meeting demand for electricity than do tranditional power plants.

From the fact that one cost has gone down while another has risen, it does not necessarily follow that the first is now lower than the second. In particular, if the cost of producing electric power at photovoltaic power plants twenty years ago was more than then times the corresponding cost for traditional plants, then the fact that it is now one-tenth what it was is not sufficient to show that it is now lower than the corresponding cost for traditional plants, even though we are told in Premise 2 that the cost for traditional plants has increased. To conclude from the premises given in the argument that photovoltaic power plants now offer a less expensive approach than do traditional power plants, we need to know how the costs of the two methods of production were related 20 years ago – specifically that the cost of producing power at photovoltaic plants was less than 10 times the cost of producing it at traditional plants. (D) gives this information and is, thus, the credited response.

A.        is incorrect because it tells us about only one of the two costs, not about how the two were related 20 years ago. It in effect restates premise 2, and premises 1 and 2 together are not sufficient for drawing the conclusion.

B.         is incorrect. The amount of electricity produced by the different kinds of plants is not at issue.

C.         is incorrect. While it is relevant tothe discussion, (C) does not provide the information about the comparative costs of the two kinds of plants 20 years ago that allows the conclusion to be properly drawn.

D.        is incorrect because the conclusion in the argument is about the present only. Whether or not the change described in (E) is expected to take place has no bearing on the claim in the conclusion that the one kind of plant offers a less expensive approach at present.

melissasun 同学解释的很清楚，这俩题中规中矩，是两个好典型题目！

117  

C----->B

A----\----C   

so  A----->B     B is the gap or bridge   

中文的解释比英文清楚多了！