Q 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, house
Holds whose microwave oven has no built-in clock use 45 kilowatt-hours per year
Less.

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.

想了半天想不明白为什么选D

请大家给点思路