In an experimental situation, a rabbit is exposed to a viral antigen to which it makes antibodies. these antibodies are then purified and injected into a human with the same viral disease. this is an example of

Passive immunization

Explanation:

Passive immunity is a situation where there is a transfer of ready-made antibodies to the recepient. In this situation, the transferred antibodies help to prevent virus and infetious diseases. The downside of this type of immunization is that, the protection it offers doesn't last long, it may last for a few weeks or a few months. We have both natural and artificial passive immunization.

In this case, since the rabbit is exposed to a viral antigen to which it makes antibodies, and the antibodies are then purified and injected into a human with the same viral disease we can say a passive immunization has taken place and it is of artificial type.

b. the carbon cycle ensures living things have a source of hydrogen