24-18 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, households whose microwave oven has no built-in clock use 45 kilowatt-hours per year less. On average, than do comparable households whose microwave oven is otherwise 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.

B) Microwave ovens with a built-in clock do not generally cost more to buy than microwave ovens without a built-in clock.

C) All households that have a microwave oven also have either a gas oven or a conventional electric oven.

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

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.

此题选D，蒙对的，其他的怎么排除？想不太明白的说。

题干中比较：微波炉有无内置表的用电情框。

A：比较的是有无微波炉的情况，而不是微波炉有无内置表的情况，无关。

B：比较哪种更贵。无关

C：很明显无关

D：没有内置表的微波炉不太可能有外置的表（同样也耗电）。取非，weaken结论。

E：无关

斑竹强，谢了！！！！