What Specific Challenge Does Trypanosoma Brucei Present to the Immune

What specific challenge does Trypanosoma brucei present to the immune system?

A) It frequently changes its antigens, staying one step ahead of the host's antibody response.
B) It specifically attacks B-lymphocytes preventing activation and antibody production.
C) It specifically attacks T-lymphocytes preventing their activation and crippling the cell-mediated immune response.
D) Its antigens are not recognized by B and T-lymphocytes so these host defense cells don't respond to the infection.