All of these are effective
Answer: every two years or so.
Answer:
They protect you against illness and disease, they are also part of the immune system.
Explanation:
They flow through your bloodstream to fight viruses, bacteria, and other foreign invaders that threaten your health.
When you get sick, your body makes more white blood cells to fight the bacteria, viruses, or other foreign substances causing your illness. This increases your white blood count
Hope this helps
Mark brainliest if it helps
It's d because he might be depressed