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, is 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 if which one of the following is assumed?
CPN (CostPhotovoltaicNow)=0.1CPB (CostPhotovoltaicBefore)
CFN (CostFossilNow)>CFB (CostFossilBefore)
To be able to draw a conclusion that compares CPN and CFN we need an assumption that relates CPB and CFB:
(A) The cost of producing electric power at traditional plants has increased over the past 20 years.
We already know that CFN is more than CFB. It doesn't matter if CF has been increasing over 20 years.
(B) Twenty years ago, traditional power plants were producing 10 times more electric power than were photovoltaic plants.
We need (unit) cost figures. If we know quantity without how much total cost each type of plants have, we can't get to the cost comparison.
(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 20 times the cost of producing power at traditional plants.
It's close, but still a little different from the real assumption that is needed. It might or might not render the conclusion correct.
(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.
Not strong enough for saying CP today is smaller than CF today. If CP before is a million times more than CF before, even if it has been decreasing and will decrease further, it might not be cheaper today. What's going to happen in the future really is irrelevant to the conclusion as of today.
D is not good enough, but all the others are irrelevant. I would say this question is not designed properly. If the number in D is changed to 10, or if it is specified in the stem that the cost of fossil plant has doubled today, then D would be a perfect choice.
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