17. The primary purpose of the passage is to
explain the differences in the working of a heat pump when the outdoor temperature changes
contrast the heating and the cooling modes of heat pumps
describe heat pumps, their use, and factors affecting their use
advocate the more widespread use of heat pumps
expose extravagant claims about heat pumps as false
18. The author resolves the question of whether heat pumps run counter to the principle of energy conservation by
carefully qualifying the meaning of that principle
pointing out a factual error in the statement that gives rise to this question
supplying additional relevant facts
denying the relevance of that principle to heat pumps
explaining that heat pumps can cool, as well as heat, room air
19. It can be inferred from the passage that, in the course of a heating season, the heating capacity of a heat pump is greatest when
heating is least essential
electricity rates are lowest
its compressor runs the fastest
outdoor temperatures hold steady
the heating demand surges
20. If the authors assessment of the use of heat pumps is correct, which of the following best expresses the lesson that advertisers should learn from this case?
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