The ans should be B. i.e. (11)* The no of 1s should always be even so in this way they can always be represented as:2x+4y where x and y are >=0
(11)*={epsilon,11,1111,11111 so on} epsilon if x=y=0
for eg: for 11 x=1 y=0 for 1111 x=0 y=1 111111x=1 y=1 and so on....