4. Gabriele notices that the number 2022 is written with 3 identical digits (different from 0) and one digit 0. How many natural numbers of 4 digits are there in total that are written with 3 identical digits (different from 0) and one digit 0?
(A) 21
(B) 22
(C) 24
(D) 25
(E) 27
Problem 4. The correct answer is (E).

First, we choose the position of the digit 0 (3 possibilities), then which digit, different from 0, occupies the other three positions (9 possibilities). The possible choices are therefore $3 \cdot 9=27$.