please help! the reading exercise's answer confuses me

[san2612]

The reading:

Making an efficient ice box was not as easy as we might now suppose. In the early
nineteenth century, the knowledge of the physics of heat, which was essential to a
science of refrigeration, was rudimentary. The commonsense notion that the best
icebox was one that prevented the ice from melting was of course mistaken, for it was
the melting of the ice that performed the cooling. Nevertheless, early efforts to
(15) economize ice included wrapping the ice in blankets, which kept the ice from doing its
job. Not until near the end of the nineteenth century did inventors achieve the delicate
balance of insulation and circulation needed for an efficient icebox.

(The reading TOefl 500)

1. According to the information in the second paragraph, an ideal

icebox would
(A) completely prevent ice from melting
(B) stop air from circulating
(C) allow ice to melt slowly
(D) use blankets to conserve ice
I chose A but the answer key is C. which is correct

[SoothingDave]

The commonsense notion that the best
icebox was one that prevented the ice from melting was of course mistaken, for it was
the melting of the ice that performed the cooling.

What does this sentence say?

[san2612]

it means an ideal icebox would completely prevent ice from melting, doesn't it?

[SoothingDave]

No, it doesn't. It says that notion is mistaken.

It also says that the melting ice performs the cooling. Think about it. If the ice does not melt, there is no transfer of heat.