Let's review the options:
A. 169-26y+y^2 can be factorised into (13-y)(13-y)
B. 81+18y+y^2 can be factorised into (9+y)(9+y)
C. 64+8y+y^2 cannot be factorised into double brackets
D. 25+10y+y^2 can be factorised into (5+y)(5+y)
Therefore your answer is the odd one out, C.
