White blood cells reside beyond circulating blood

Steps:

• White blood cells (leukocytes) originate in bone marrow and circulate in blood.
• They migrate to tissues for immune surveillance and response.
• Storage occurs in lymph nodes and spleen for rapid deployment.
• Thus, they are present in lymph, tissues, and organs like spleen and bone marrow.

Why A is correct:

• White blood cells are found in all three locations (1: lymph system, 2: tissues, 3: bone marrow/spleen) as part of the immune system's distributed network.

Why the others are wrong:

• B excludes 3, but bone marrow produces and stores WBCs.
• C excludes 2, but WBCs infiltrate tissues during infections.
• D excludes 1, but lymph carries WBCs between nodes and blood.

Final answer: A