For each positive digit D and positive integer k, we use the symbol D_{(k)} to represent the positive integer having exactly k digits, each of which is equal to D. For example, 2_{(1)}=2 and 3_{(4)}=3333. There are N quadruples (P, Q, R, k) with P, Q and R positive digits, k a positive integer with k \leq 2018, and P_{(2 k)}-Q_{(k)}=\left(R_{(k)}\right)^{2}. The sum of the digits of N is
Answer Choices
A. 10
B. 9
C. 11
D. 12
E. 13