15. Caterina starts writing all positive integers, one after the other: 12345678910111213... Which digit will occupy the 2017th position?
(A) 8
(B) 5
(C) 1
(D) 7
(E) 2
(15) The correct answer is $(D)$.

Caterina writes 9 single-digit numbers, for a total of 9 digits. Then she writes 90 two-digit numbers, those between 10 and 99 - for a total of 180 digits. At this point, she will have written 189 digits, and there will be $2017-189=1828$ digits left to write to reach the 2017th.

The next numbers are three-digit numbers. Since $1828=3 \cdot 609+1$, the digit in the 2017th position will be the first digit of the six hundred and ninth three-digit number. This number is 709, and its first digit is 7. Problem proposed by Carmelo Di Stefano.