Which of the following most logically completes the passage?
Thick concrete walls insulate well and houses built with them cost less to heat and cool than wooden houses do. Researchers compared a wooden house with a concrete house that was otherwise identical in every significant way (sun exposure, size, heating and cooling system, etc.). Over a year, monthly energy costs averaged $55 less for the concrete house. In practice, most people choosing a concrete house over a wooden one would probably realize still greater monthly savings on energy, because ________. The passage presents some comparative information about the cost of heating houses built with concrete walls and that of heating wooden houses.
It then states a conclusion:
In practice, most people choosing a concrete house over a wooden one would probably realize still greater monthly savings on energyWe can tell that that statement is a conclusion by noticing that it's followed by "because __________."
In this type of context, "because" is an evidence marker, and what follows "because" is a premise that supports the conclusion that precedes "because."
So, the choice that fills the blank must be a premise that supports the conclusion, "In practice, most people choosing a concrete house over a wooden one would probably realize still greater monthly savings on energy."
A - the houses in the survey were built in a region that has winters that are slightly cooler on average, and summers that are slightly warmer on average than is typical of most regions in the countryThis choice provides support for the wrong conclusion.
The conclusion we need to support involves people
saving on energy because of having a concrete house rather than a wooden house. On the other hand, this choice indicates that people would simply
spend less on energy, on average, regardless of what type of house they have.
After all, if this choice is true, then, on average, people would likely spend less in winter and summer to heat and cool their houses respectively than was spent to heat and cool the houses in the survey. After all, given what this choice says, average outdoor temperatures are less extreme than the outdoor temperatures in the region where the houses in the survey were located, and it costs less to heat and cool a house when outdoor temperatures are less extreme.
At the same time, the differences in temperature mentioned by this choice would not cause people who have concrete houses to save more. Spending less because of less extreme outdoor temperatures is not the same as saving because of having a concrete house. In fact, being in a region where outdoor temperatures are less extreme would allow people who have wooden houses to spend less as well.
Eliminate.
B - the heating and cooling systems in the houses in the survey were typical of those found in the average house in the area in which they were built If antyhing, this choice casts doubt on, rather than supports the conclusion.
After all, if this choice is true, then the houses in the survey are similar to average houses. The fact that they are similar in this way indicates that the savings achieved by people in average houses would be about the same as, rather than greater than, the savings achieved in the case of the concrete house in the survey.
Eliminate.
C - the wood used in building the wooden house in the survey had high insulating properties created by an experimental treatment that is generally regarded as too expensive for residential constructionThis choice is interesting.
If this choice is true, then the wooden house in the survey was better insulated than the average wooden house. Of course, in that case, having that concrete house rather than the wooden house in the survey resulted in less-than-average savings because the difference between the insulating properties of the concrete and the wood in those houses was less than average.
So, if this choice is true, the average person would save more than was saved in the case of the survey houses by having a concrete house rather than a wooden house because, normally, the difference between wood and concrete is greater.
So, this choice supports the conclusion.
Keep.
D - the energy efficiency of houses with concrete walls varies greatly depending on the thickness of the walls, with relatively thin concrete walls providing only slightly greater energy efficiency than well-built wooden wallsThis choice would support the conclusion if the passage said that the concrete house in the survey had relatively thin walls. After all, in that case, people whose houses have average, rather than relatively thin, concrete walls would save even more by having concrete walls rather than wooden walls.
At the same time, the passage doesn't say that the house in the survey had relatively thin concrete walls. So, for all we know, it had average concrete walls. In that case, the fact that relatively thin concrete walls provide only slightly greater energy efficiency than wooden walls is irrelevant. After all, in that case, there's no reason to believe that the average house with concrete walls has thicker walls than the concrete house in the survey.
Eliminate.
E - for the first forty years or so after they are built, maintenance costs for houses built with thick concrete walls tend to be lower than maintenance costs for comparable houses built with wooden wallsThe conclusion that the correct answer must support is about energy costs, not maintenance costs or total costs. So, because maintenance costs have no clear effect on energy costs, this information about maintenance costs has no bearing on the conclusion.
Eliminate.
Correct answer: C