Answer:
The safety and effectiveness of vaccines are under constant study. Because vaccines are designed to be given routinely during well-child care visits, they must be extraordinarily safe. Safety testing begins as soon as a new vaccine is contemplated, continues until it is licensed, and is monitored indefinitely after licensure.
Explanation:
I believe the answer is (B)
<span>a complex series of feeding relationships with many organisms interacting and depending on each other </span>
Methanogens can be found in B.human intestines
Roots of plants and synthetic fertilizers can contain oxygen or come into contact with oxygen.
