168.17.07.255 {Class B}
given that, it is DBA which means all host bits of a subnet should be raised to 1.
last 2 octals = 0000 0111.11111111
a) 255.255.248.0
last 2 octals = 11111 000. 00000000 {if this is network mask then, its DBA of 0th subnet }
b) 255.255.252.0
last 2 octals = 111111 00.00000000 {if this is network mask then, its DBA of 1st subnet }
c) 255.255.254.0
last 2 octals = 1111111 0. 00000000 {if this is network mask then, its DBA of 3rd subnet }
d) 255.255.255.0
last 2 octals = 11111111.00000000 {if this is network mask then, its DBA of 7th subnet }
Hence , all are correct.