In Western economies, more energy is used to operate buildings than to operate transportation. Much of the decline in energy consumption since the oil crisis of 1973 is due to more efficient use of energy in homes and offices. New building technologies, which make lighting, heating, and ventilation systems more efficient, have cut billions of dollars from energy bills in the West. Since energy savings from these efficiencies save several billion dollars per year today, we can conclude that 50 to 100 years from now they will save more than $200 billion per year (calculated in current dollars).
NOW: new tech -> cut cost
FUTURE: 50 to 100 years from now -> SAVE > $200B
The logical chain seems very legitimate and has no GAP here. So it must be the Defender Assumption type, which requires eliminating possibility that can break down the argument.
As we can see from the short-version of the argument. The author argued that just because the tech is currently cutting cost, it'll do the same in the future. Is that so? What If resources become scarce, leading to higher in cost of creating those techs? Then we might not be able to save money in the next 50 to 100 years.
The correct answer must eliminate this or similar possibilities.
On which one of the following assumptions does the argument rely?
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(A) Technology used to make buildings energy efficient will not become prohibitively expensive over the next century.
Ah ha. This matches our thought. Hang on to this.
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(B) Another oil crisis will occur in the next 50 to 100 years.
No where in the argument says that there will be another oil crisis in the future. (B) is out.
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(C) Buildings will gradually become a less important consumer of energy than transportation.
Yeah that maybe true. But does it affect the conclusion? If this is not true, the conclusion still holds true. (C) is out.
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(D) Energy bills in the West will be $200 billion lower in the next 50 to 100 years.
Okay, lower bill. However, what if the cost of technology is greater than $200B? Then we end up not saving anything. (D) is out.
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(E) Energy-efficient technologies based on new scientific principles will be introduced in the next 50 to 100 years.
We only care about the tech that have already been created. Future tech is irrelevant.
A is left. (A) is our correct answer.