Final answer:
Chemokines CCL21 and CXCL13 are responsible for attracting B cells to the HEV and lymph nodes respectively. The correct option is d.
Step-by-step explanation:
Chemokines are chemotactic cytokines that recruit specific subsets of leukocytes to sites of infection, damaged tissue, and inflammation. These chemokines play a significant role in guiding B cells to the high endothelial venules (HEV) and lymph nodes. The correct answer to the question "Chemokines____ and ____attract B cells to the HEV and lymph node respectively." is option d. CCL21 ; CXCL13. CCL21 is involved in the attraction of B cells to the HEV, whereas CXCL13 plays a crucial role in directing them to the lymph nodes. Hence, d is the correct option.