Which of the Following Expressions Always Represents an Irrational Number $\sqrt{a}$

Which of the following expressions always represents an irrational number?

A) $\sqrt{a}$ , where a is an odd number
B) $\sqrt{p}$ , where p is a prime number
C) b², where b is an irrational number
D) c + d, where c and d are irrational numbers