The correct option is A 12-13 days
The WBCs or leukocytes handle more complex functions. They are the defense mechanism of the human body for fighting infections. There are different types of WBCs with varied life cycles and distinct functions. White blood cells also produce a special protein called antibody which recognize and fight the presence of foreign elements in the body. The life span of WBC is 10-15 days depending on body. Thus, option A is correct.