Which of the following statements is correct?

Select one:

a$.$ Set B of all strings of equal number of a$\text{'}$s and b$\text{'}$s deines a regular language

b$.$ L $($A$*$ B$*)\backslash$cap B gives the set A

c$.$ A$=[$If a$^$n b$^$n $|$n $=0,1,2,3.)$ is regular language

d$.$ None of these