Q19 Which of the following are not regular
A)Strings of even number of a's.
B)Strings of a's , whose length is a prime number.
C)Set of all palindromes made up of a's and b's.
D)trings of a's , whose length is a perfect square.
1) A and B only 2) A,B,C only
3) B,C and D only 4) B and D only