Final answer:
The correct answer is c.) Searching for information on white blood cell activity would lead the researcher to information about antigen-antibody reactions.
Step-by-step explanation:
The phrase that would best lead the researcher to information about antigen-antibody reactions is c. white blood cell activity.
Antigen-antibody reactions involve the interaction between antigens (foreign substances) and antibodies (proteins produced by white blood cells). These reactions play a crucial role in the immune response, as antibodies bind to specific antigens to neutralize or eliminate them.
By searching for information on white blood cell activity, the researcher would be able to find relevant information about antigen-antibody reactions and their role in the immune system.