Cellular Immunity Response
As you can simply find on Wikipedia, the cellular immunity, or Cell-mediated immunity, 


  is an immune response that does not involve antibodies, but rather
  involves the activation of phagocytes, antigen-specific cytotoxic
  T-lymphocytes, and the release of various cytokines in response to an
  antigen.


The answer (c) (destroying the bacteria cell by enzyme) refers to the phagocytes, cells that contain many enzymes, like lysozymes. Those funny enzyme can destroy the bacteria cell's wall.

Actually, I think that the answer (d) could be right, but it's not complete. In fact not every enzymes works on the cell's wall!