The correct option is C Lymphocytes
Acquired immunity is a type of immunity which is not present at birth. It is learned. As a person's immune system encounters various antigens, the components of acquired immunity find the best way to attack each antigen and begins to develop a memory for that antigen. It is also called specific immunity. Acquired immunity takes time to develop after initial exposure to a new antigen.
Lymphocytes are the type of white blood cell responsible for acquired immunity. Acquired immune response begins with antibodies, produced by B cells or B lymphocytes.
Thus, the correct answer is the option (D), 'Lymphocytes'.