3. The average of five unequal natural numbers is 15, and the median is 18. Then the maximum value of the largest number among these five numbers is ( ).
(A) 35
(B) 36
(C) 37
(D) 38
3. C.

Let the other four numbers among these five numbers be $a, b, c, d$, and $a<b<18<c<d$. Then, $a+b+c+d=57$.

To maximize $d$, $a, b, c$ need to take their minimum values, so let $a=0, b=1, c=19$. In this case, $d=37$.