The system is a contributor to both innate and humoral immunity that requires sequential activation.

The correct answer is: The complement system.

Explanation:

-The complement system can also be known as the complement cascade is one of the fundamental components of the system that helps the organism defend from pathogen agents.

-It is known as the complement system because it helps antibodies in the task of clearing microbes and damaged cells, and attacking pathogen agents.

-The complement system is a part of the inmune system as is brought into action via activation of the adaptive inmune system.

In conclusion, the complement system is a contributor to both innate and humoral inmunity that requires sequential activation.

even though you have attached neither the chart nor the generalizations, i have located them online. the right answer is d, since they are asking you about a generalization. you can only infer from the chart that between 2008 and 2009 the number of employed workers decreased significantly (from over 115 millions to 107 millions approximately), which signals some type of economic crisis.  

answer; participant observation method;