Ok, value of $\binom{6}{6}$ is 1.
so here n is 6, according to d option (n==0) && (m==n), (n==0) is also should be true then whole statement return 1, but here it will not return 1.
while taking to option c. (n==0)||(m==n) the whole statment return 1.
same you also check with $\binom{6}{0}$