Lymphocytes produce special proteins against foreign invaders called

antibodies

Explanation:

Lymphocytes defend the human body from any foreign element (known as antigen) by producing antibodies. Each lymphocyte, also known as B cell produce specific antibody.  

A lymphocyte gives rise to plasma cell which acts like a factory of antibodies.  

There are two type of lymphocytes which act against the antigens in following ways –  

B lymphocytes – they kill antigens by producing antibodies

T lymphocytes – They act against the antigen in two ways a) by producing  lymphokines which signal other cells and b) directly destroy targeted cells on direct contact.

d is the answer

sorry if its wrong!

primary succession occurs in essentially lifeless areas regions in which the soil is incapable of sustaining life as a result of such factors as lava flows, newly formed sand dunes, or rocks left from a retreating glacier. secondary succession occurs