Correct choice is (b) Diapedesis
The best I can explain: When a WBC or a neutrophil, in this case, is moving out of the blood vessels, the size of the pores in the blood vessels is too small as compared to the size of the WBC. Thus, for the WBCs to come out, they squeeze out a tiny amoeboid leg out if the pore and slowly move out. This process is diapedesis.