Solution:The pattern followed here is :{1st letter - 7 = 2nd letter}, {2nd letter - 6 = 3rd letter}, {3rd letter - 5 = 4th letter} & {4th letter - 4 = 5th letter}
HAUPL → (H - 7 = A), (A - 6 = U), (U - 5 = P) & (P - 4 = L)
YRLGC → (Y - 7 = R), (R - 6 = L), (L - 5 = G) & (G - 4 = C)
ATNIE → (A - 7 = T), (T - 6 = N), (N - 5 = I) & (P - 4 = E)
But,
GZTNK → (G - 7 = A), (Z - 6 = T), (T - 5 ≠ N) & (N - 4 ≠ K)
Hence, GZTNK is the correct answer.