A3. David has come up with a three-digit natural number with three different digits. He replaced each digit of this number with a letter to get the word $E N A$, which represents his number. He noticed that for his number, $c \cdot E N A=$ 2331, where $c$ is some natural number. What is the value of the number $c$?
(A) 3
(B) 7
(C) 9
(D) 21
(E) 37

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A3. The positive divisors of the number $2331=3^{2} \cdot 7 \cdot 37$ are $1,3,7,9,21,37,63,111,259,333,777$ and 2331. Among them, only 259 is a trimest natural number with three different digits. Therefore, $E N A=259$ and thus $c=2331: 259=9$.