To measure T-cell response to a particular antigen,

To measure T-cell response to a particular antigen,
 
  a. the antigen is added to a purified population of T cells, and tritiated thymidine is added to measure T-cell proliferation
  b. the antigen is added to T cells and antigen-presenting cells, and tritiated thymidine is added to measure T-cell proliferation
  c. the antigen is added to T cells and antigen-presenting cells, and Chromium 51 is added to measure T-cell proliferation
  d. mitogen and the antigen is added to mononuclear cells, and tritiated thymidine is added to measure T-cell proliferation