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) Strings of a’s whose length is a perfect square.

• A. (A) and (B) only
• B. (A), (B) and (C) only
• C. (B), (C) and (D) only
• D. (B) and (D) only