a) All words on ={a,b} that the last two letters are different. Example: aabba,abbab b) All words on ={a,b,c} that (na(w)+2nb(w)nc(w))mod9=2. c) All words on ={0,1} that the remainder of the represented binary number by 8 is 5 . d) All words on ={a,b,c} that between each two substrings 'ab', we have a substring 'bc' Example: bbabaabcbbabcc, abbcab