Question 74·Medium·Command of Evidence
The passage below is adapted from an article about trends in renewable energy.
(1) Over the past decade, global investment in solar power has surpassed that of any other renewable energy source.
(2) Analysts once viewed large-scale solar farms as prohibitively expensive.
(3) But improvements in manufacturing processes have cut the price of photovoltaic panels by nearly 90 percent since 2010.
(4) As costs have dropped, installation rates have soared, doubling every three years.
(5) These rapid changes have prompted many governments to revise their energy projections.
(6) In 2012, for instance, the International Energy Agency predicted that solar would supply 16 percent of world electricity by 2050.
(7) Just eight years later, the agency adjusted that figure to 33 percent, citing continued declines in production costs.
(8) Because of these declines, solar power is now cheaper than newly built coal plants in most regions.
(9) For consumers, the shift is already visible: rooftop arrays once reserved for the wealthy are increasingly common even in middle-income neighborhoods.
(10) As one energy economist notes, "The sun is delivering a remarkably affordable dividend."
(11) If current trends persist, solar power could become the dominant global electricity source within two decades.
Which choice provides the best evidence for the claim that falling production costs have made solar power broadly affordable?
For command-of-evidence questions, first rephrase the claim in your own words and underline its key parts (such as cause and effect). Then, before looking at the answer letters, quickly scan the cited lines in the passage and ask for each: does it explicitly show all parts of the claim, not just repeat one word? Eliminate choices that only mention cost changes, only mention affordability, or that focus on projections or future trends without clearly connecting the specific cause and effect. Pick the line that most directly and completely supports the claim as written, avoiding answers that require you to infer a connection the passage does not state.
Hints
Break the claim into parts
Underline in the question stem what happened ("falling production costs") and what result that led to ("broadly affordable"). You need evidence that clearly shows both the cause and the effect.
Scan for both cost and affordability
Look at each line reference and ask: does this sentence talk about declining production costs and also show that solar is now cheap or widely accessible, not just that it is more common or more highly projected?
Watch out for partial matches
Some choices talk about dropping costs but not affordability; others mention affordability without saying anything about costs falling. Focus on the one that clearly connects the cost declines to how cheap or widely available solar has become for ordinary people or in many regions.
Step-by-step Explanation
Understand what the claim is saying
The claim says: falling production costs have made solar power broadly affordable. That means the best evidence must show both:
- a drop in production costs (cause), and
- that solar is now cheap or accessible for many people or areas (effect).
Translate the claim into what you need to find
Rephrase the claim in your own words: because it has become cheaper to produce solar power, many people can now afford it. So, when you look at the answer choices, ask for each quoted line:
- Does it mention that costs are going down?
- Does it also show that solar is now cheap or widely accessible (for most regions or ordinary consumers), not just that it’s being installed more or predicted to grow?
Eliminate choices that don’t show broad affordability
Now check the options:
- Choice A (lines 4–5) talks about dropping costs and soaring installation rates, plus governments revising projections. It connects lower costs to higher usage and planning, but it never says solar is cheap or affordable to ordinary people or across many regions.
- Choice B (lines 6–7) explains how an agency increased its prediction of how much electricity solar will provide because of lower production costs. That links costs to future energy share, not to affordability for consumers.
- Choice D (lines 10–11) includes the word "affordable" and mentions solar could become dominant, but it does not mention falling production costs at all. It shows that solar is affordable, but not because production costs fell.
None of these fully show both parts of the claim at the same time.
Confirm the choice that matches both parts of the claim
Choice C (lines 8–9) says that because of these declines (the falling production costs mentioned earlier), solar is now cheaper than newly built coal plants in most regions, and that rooftop systems once only for the wealthy are now common in middle-income neighborhoods. This directly links declining production costs (cause) to solar being cheaper than coal in many places and affordable enough for ordinary, middle-income consumers (broad affordability). Therefore, Choice C is the best evidence.