This is basically a question of variable length subnet masking.
here, 8 hist id bits are divided in the following way to get exactly 3 subnets and not 4-->
10000000
and
00000000 , 01000000
or
00000000
and
11000000 , 10000000
the subnets will have following range of ip addresses- > (0 to 127), (128 to 191),(192 to 254).
DBAs are respectively->
1) 255.255.255.127
2)255.255.255.191
3)255.255.255.254
so ans is B