It depends on the case, but usually two variables should be in a controlled experiment.
Answer:
Dictionary Definitions:
the number or quantity of people or things that can be conveyed or held by a vehicle or container.
If it's ecology: the number of people, other living organisms, or crops that a region can support without environmental degradation.
Explanation:
I don't know if you're talking about an ecosystem or not but that's the dictionary definition (:
Answer:
C
Explanation:
Becuase fom a vaccine you are recieving antibodies by another animal or human donor.
D is unlinkely since it describes how the mother is nursing the baby, so nothing directly mentioning of the baby recieving any antibodies. The other options also talk about how the body creates its own antibodies, which isn't passive immunity.
