why can not we have option B as our answer? please explain in detail.
Welcome to GMAT club!
I'm glad to help you this question. GENERAL METHOD
This is “evaluate the argument
”, one of the most difficult type of CR questions. To attack this question:
- First, determine the conclusion is KEY
. If you do not know what the argument wants to conclude. How can you evaluate its argument?
- Next, you can use general methods to eliminate wrong answers (out of scope, reverse answer, …)
- When you narrow to TWO options and don’t know which one is correct, you can apply “variance method”.
How to use this strategy? The answer choices always have the question “whether X can help Y……?”, for instance. Just plug in “yes”, or “no” to the question. For example: X can help Y…., and X cannot help Y….. If the two answers (Yes & No) make the author changes his/her conclusion. This option choice is correct.ANALYZE THE STIMULUS:
Fact: New coal-burning plants usually comply with the law by installing expensive equipment to
filter sulfur dioxide from their emissions.
Fact: installing cleaning equipment that chemically removes most sulfur from coal before combustion is less expensive.Conclusion:
These new plants could save money by installing cleaning equipment.Pre-thinking:
Are there any cost other than “equipment cost”? For example: administration cost, labor cost, maintenance cost, etc… We should calculate TOTAL COST
to make a final conclusion.ANALYZE EACH ANSWER
A. Whether existing oil-burning plants are required to filter sulfur dioxide from their emissions Wrong.
Nothing about “costs”. Out immediately.
B. Whether the expense of installing the cleaning equipment in a new plant is less than the expense of installing the cleaning equipment in an older plant Wrong.
We are comparing expense of “cleaning equipment” vs “filtering equipment”. B only compares expense of installing “cleaning equipment” in new plan and old plan.
It does not help you to compare expense between two options “cleaning equipment” vs “filtering equipment”. Hence, B is wrong.
C. Whether the process of cleaning the coal is more expensive than the process of filtering the emissions Correct. If “YES”.
the process of cleaning the coal is more expensive
than the process of filtering the emissions ==> the new plants could not save
money by installing cleaning equipment. If “NO”.
the process of cleaning the coal is NOT more expensive
than the process of filtering the emissions ==> the new plants could save
money by installing cleaning equipment.
Thus, C definitely can help to “evaluate” the conclusion. Hence, C is correct.
D. Whether lawful emissions of sulfur dioxide from coal-burning plants are damaging the environment Wrong.
Nothing about “costs”. Out immediately.
E. Whether existing plants that use the filtering equipment could replace this equipment with the cleaning equipment and still compete with new plants that install the cleaning equipmentWrong. TEMPTING but wrong. If “Yes”.
Existing plants that use the filtering equipment COULD replace
this equipment with the cleaning equipment .......... Okay, existing plants can replace their equipment with cleaning equipment. How can we compare between “cleaning equipment” and “filter equipment”, which one is cheaper? If “No”.
Existing plants that use the filtering equipment COULD NOT replace
this equipment with the cleaning equipment….. Okay, existing plants cannot replace their equipment with cleaning equipment, they still use filtering equipment. How can we compare between “cleaning equipment” and “filter equipment”, which one is cheaper?
Clearly, E just says the existing plants can or cannot replace the filtering equipment with cleaning equipment. That's it. E does not help anything to “evaluate” which one could help to save money
. Hence, E is wrong
Hope it helps.
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