The possible value of B2 B1 B0 if i/p is applied to 8x3 encoder :-
if input is O o 0 0 0
if input is O 1 0 0 1
if input is O 2 0 1 0
if input is O 3 0 1 1
if input is O 4 1 0 0
if input is O 5 1 0 1
If input is O 6 1 1 0
If input is O 7 1 1 1
So, B2==1 if either i/p is applied O4+O5+O6+O7
B1==1 If either i/p is applied O2+O3+O6+O7
B0==1 If either i/p is applied O1+O3+O5+O7.
As per given logical expression in question only B2 and B1 is correct. So, answer is B.
Correct me i am wrong.