Critical Reasoning

mgmt_gmat wrote:Most household appliances use electricity only when in use. Many microwave ovens,
However, have built-in clocks and so use some electricity even when they are not in Use. The clocks each consume about 45 kilowatt-hours per year. Therefore, house Holds whose microwave oven has no built-in clock use 45 kilowatt-hours per year Less. On average, than do comparable households shoes microwave oven is other-Wise similar but has a built-in clock.

Which of the following is an assumption on which the argument depends?

A. Households that do not have a microwave oven use less energy per year, on average, than do households that have a microwave oven.
Incorrect : Comparison of energy use between owners and non-owners of microwave is out of scope.

B. Microwave ovens with a built-in clock do not generally cost more to buy than microwave ovens without a built-in clock.
Incorrect : Cost of microwave ovens with built in clock and without built in clock is irrelevant.

C. All households that have a microwave oven also have either a gas oven or a Conventional electric oven.
Incorrect : Gas/Conventional oven blah blah blah out of scope !!

D. Households whose microwave oven does not have a built-in clock are no more likely to have a separate electric clock plugged in than households whose microwave oven has one.
Correct : This fills the logical gap between the premise and the conclusion by assuming that if households whose microwave oven does not have a built in clock also buy electric clocks, then they consume electricity no less than households who use microwave with built in clock.

E. There are more households that have a microwave oven with a built-in clock than there are households that have a microwave oven without a built-in clock.
Incorrect : Clearly out of scope