Final answer:
The correct statement is option b. TH1 cells do not produce IL-3 and IL-9 which recruit mast cells.
Step-by-step explanation:
The correct statement in regards to CD4 activation and differentiation into TH1 and TH2 cells is option b. TH1 cells produce IL-3 and IL-9 which do not recruit mast cells. TH2 cells, on the other hand, produce IL-5 which recruits eosinophils, IL-13 which increases production of epithelial cells, and TH1 cells secrete Interferon g which activates macrophages.