Please look at this question.
"Bertoia Peters, a famous furniture designer, assured his clients that his creations are the ____ furniture that money can buy"

(A) fine (B) finest

The correct answer is (B)finest. But I think I can put "(A) find there because there is no additional words on what the writer is comparing his creations with. I mean there is neither contractive nor comparative words at all in the sentence. So I think I can use (A),too.

Could you explain to me why I can't use (A) fine just as a adjective there ?

Thanks in advance.
There is no grammatical reason why fine is not used. It just isn't, and that's why finest is the right answer.

The reason is that his creations are not just the fine, they are the finest furniture that money can buy.There are many other items of furniture that money can buy; of all the items of furniture that money can buy, Peters's are the finest.
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Even though fine could be used, finest has to go in this expression. That money can buy is an expression used to let the listener know that there is indeed no better item that could have been purchased. More Examples:

This is the fastest car that money can buy.
During the eighties, this was the prettiest dress that money could buy.

Although the word finest is often used, it can be substituted with other words in their superlative form. Also look at its usage below.

We have the best computer that money can buy.
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Thank you so much for your kind explanation,Ms.Cynthia.
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