opt a) 3digit prime num.so it is finite(101,103.....997).so it is regular
opt b) we cant construct dfa for |no.of a's-an.of b's|<=2. for each prefix.
opt c)we can contruct dfa for more no.of 1's than 0's like that possible to construct |no.of a's-no.of b's|<=4 so,it is regular
opt d) already we know that regular.
so ans is: opt B