For natural numbers $m$, $n$ if $(1-y)^m (1+y)^n = 1 + a_{_1}y + a_{_2} y^2 + ...$ and $a_{_1} = a_{_2} = 10$, then $(m, n)$ is :

Question

( A ) (35, 45)
( B ) (35, 20)
( C ) (20, 45)
( D ) (45, 35)